erplex
  • Lessons
  • Problems
  • Speed Run
  • Practice Tests
  • Skill Checklist
  • Review Videos
  • All Content
  • Landing Page
  • Sign Up
  • Login
  • erplex

    Concept Lessons

    Access comprehensive explorations for all concepts in your objective, including problems, helpful visuals, and AI features.

    What you'll find in every lesson:

    High-quality explanations: Each lesson is carefully crafted to help you truly understand the concept, not just memorize it.

    Checkpoint exercises: Practice as you learn with interactive problems designed to reinforce your understanding.

    AI-powered discussions: Engage with thought-provoking questions that help reveal your misconceptions.

    What you'll find in every lesson:

    High-quality explanations: Each lesson is carefully crafted to help you truly understand the concept, not just memorize it.

    Checkpoint exercises: Practice as you learn with interactive problems designed to reinforce your understanding.

    AI-powered discussions: Engage with thought-provoking questions that help reveal your misconceptions.

    Concept Lessons

    Access comprehensive explorations for all concepts in your objective, including problems, helpful visuals, and AI features.

    85 Lessons Available

    What you'll find in every lesson:

    High-quality explanations: Each lesson is carefully crafted to help you truly understand the concept, not just memorize it.

    Checkpoint exercises: Practice as you learn with interactive problems designed to reinforce your understanding.

    AI-powered discussions: Engage with thought-provoking questions that help reveal your misconceptions.

    What you'll find in every lesson:

    High-quality explanations: Each lesson is carefully crafted to help you truly understand the concept, not just memorize it.

    Checkpoint exercises: Practice as you learn with interactive problems designed to reinforce your understanding.

    AI-powered discussions: Engage with thought-provoking questions that help reveal your misconceptions.

    Cartesian plane & lines

    3 concepts with notes

    Distance, Midpoint, & Gradient

    Distance between two points, midpoint of two points, and finding gradient using two points

    Start Lesson

    Equations of a Line

    Gradient-intercept form, point-gradient form, vertical lines, horizontal lines, standard form of a line

    Start Lesson

    Line Intersections & Systems of Equations

    Parallel and perpendicular lines, intersection of 2 straight lines, solving a two-variable system of equations

    Start Lesson

    Function Theory

    3 concepts with notes

    Functions and their properties

    Domain and range of functions, function as a model, interval notation

    Start Lesson

    Function Graphs

    Graphing functions with a calculator, characteristics of a function, even and odd functions, x and y intercepts, horizontal and vertical asymptotes, maxima and minima

    Start Lesson

    Function Composition & Inverses(Plus Only)

    Composing functions, inverse functions, graphing and evaluating inverse functions, computing inverses and domain restrictions

    Upgrade to Plus

    Quadratics

    2 concepts with notes

    Foundations of Quadratics

    Vertex, standard, and factored form, axis of symmetry, concavity, quadratic formula

    Start Lesson

    Applications of Quadratics

    Evaluating the discriminant, sum and product of roots, quadratic inequalities, quadratics of other forms

    Start Lesson

    Exponents & Logarithms

    4 concepts with notes

    Exponential Algebra

    Exponents, properties of exponents, and solving exponential equations

    Start Lesson

    Logarithm algebra

    Definition and evaluation of logarithms, properties of logs, e and the natural log, change of base rule

    Start Lesson

    Radicals and Roots

    Nth roots, fractional and rational exponents, conjugates.

    Start Lesson

    Exp & Log functions(Plus Only)

    Graphing exponential functions, exponential growth and decay, logarithmic inverse functions.

    Upgrade to Plus

    Approximations & Error

    2 concepts with notes

    Rounding Numbers

    Rounding, significant figures, decimal places

    Start Lesson

    Scientific Notation

    Converting numbers to and from scientific notation (a×10k)

    Start Lesson

    Sequences & Series

    7 concepts with notes

    Arithmetic Sequences

    Introduction to the definition, properties, and general term of an arithmetic sequence

    Start Lesson

    Geometric Sequences

    Introduction to definition, identification, and general term of geometric sequences

    Start Lesson

    Arithmetic Series(Plus Only)

    Definition of series, formula for arithmetic series

    Upgrade to Plus

    Σ summation notation(Plus Only)

    Summation notation, properties of sums

    Upgrade to Plus

    Geometric Series(Plus Only)

    Definition and general term of geometric series, finite and infinite series, convergence

    Upgrade to Plus

    Sequence Mode (Calculator)(Plus Only)

    Working with sequences on a calculator, computations and applications of a calculator

    Upgrade to Plus

    Compounding (Appreciation & Depreciation)(Plus Only)

    Compound growth, depreciation, interest, inflation, real value

    Upgrade to Plus

    Counting & Binomials

    4 concepts with notes

    Pascal's Triangle and nCr

    Theoretical introduction to n​Cr​, or (nr​), and Pascal's triangle.

    Start Lesson

    Binomial Theorem(Plus Only)

    Using nCr​ to expand binomials like (1+2x)7.

    Upgrade to Plus

    Counting(Plus Only)

    Using permutations & combinations alongside principles to count the ways things can be selected or arranged.

    Upgrade to Plus

    Counting with Restrictions(Plus Only)

    Advanced techniques for scenarios with branches, negative counting, and permutations where items need to stay together / separate.

    Upgrade to Plus

    Proof and Reasoning

    3 concepts with notes

    Proof by deduction

    Introduction to the concept of proofs, proof by deduction, and proof with even and odd numbers.

    Start Lesson

    Proof by induction(Plus Only)

    The concept of a proof by induction with different types of examples.

    Upgrade to Plus

    Contradiction and Counterexamples(Plus Only)

    So far, we have learned to prove that statements are true. In this lesson, we learn strategies to prove that statements are not true.

    Upgrade to Plus

    Transformations & asymptotes

    4 concepts with notes

    Linear Transformations

    Vertical and horizontal translations, dilations, reflecting over axes

    Start Lesson

    Rational functions(Plus Only)

    Reciprocal functions, quadratic denominators, graphs of rational linear functions

    Upgrade to Plus

    Further Transformations(Plus Only)

    Graphing absolute value functions, squared functions, piecewise functions, graphing 1/f(x)

    Upgrade to Plus

    Modulus & Inequalties(Plus Only)

    Absolute value, inequalities of functions

    Upgrade to Plus

    2D & 3D Geometry

    5 concepts with notes

    Right angled triangles

    Pythagoras's theorem, SOHCAHTOA, finding side length from angles

    Start Lesson

    Non-right-angled triangles(Plus Only)

    Sine and cosine rules, finding general area of a triangle

    Upgrade to Plus

    Applied triangle geometry

    Angles of elevation and depression, true bearings, projections and more

    Start Lesson

    Circles: Radians, arcs and sectors(Plus Only)

    Measuring angles in radians, circumference & arc lengths and sector areas

    Upgrade to Plus

    3D solids

    Spheres, cylinders, prisms, right cones, right pyramids, and combinations of solids

    Start Lesson

    Trig equations & identities

    7 concepts with notes

    The Unit Circle

    Sine, cosine & tangent functions in the unit circle

    Start Lesson

    Trigonometric Functions

    Graphs, domain, and range of sinx and cosx, general sinusoidal functions, modeling periodic phenomena, tanx and reciprocal trig functions, inverse trig functions

    Start Lesson

    Reciprocal trig functions (Plus Only)

    The functions secx, cosecx and cotx, domain, range & graphs

    Upgrade to Plus

    Trig Equations(Plus Only)

    Solving equations involving trigonometric functions and understanding solution domains

    Upgrade to Plus

    Inverse trig functions(Plus Only)

    The functions arcsin,arccos and arctan, their domain & range & graph

    Upgrade to Plus

    Trigonometric Identities(Plus Only)

    Applications of trigonometric identities such as sin2θ+cos2θ=1, sin2θ=2sinθcosθ and more identities for HL students

    Upgrade to Plus

    Further trigonometric identities(Plus Only)

    Compound angle identities sin(A+B) and cos(A+B), double angle identity for tan2θ, and pythagorean identity for reciprocal trig functions.

    Upgrade to Plus

    Complex Numbers

    4 concepts with notes

    Cartesian form

    Arithmetic of complex numbers in cartesian form, including conjugates, and the Argand diagram (complex plane).

    Start Lesson

    Complex Modulus(Plus Only)

    Introduction, definition, and properties of the complex modulus

    Upgrade to Plus

    Mod-arg & Polar forms(Plus Only)

    rcisθ and eiθ

    Upgrade to Plus

    De Moivre's Theorem(Plus Only)

    De Moivre's Theorem for powers and roots of complex numbers.

    Upgrade to Plus

    Vectors

    6 concepts with notes

    Vector arithmetic & geometry

    Addition, subtraction and scalar multiplication, computed algebraically and geometrically

    Start Lesson

    Scalar and vector products

    Introduction and applications of vector and scalar products

    Start Lesson

    Equations of a line(Plus Only)

    Vector form, cartesian form, parametric form, modeling with vectors

    Upgrade to Plus

    Coincident, Parallel, Intersecting & Skew Lines(Plus Only)

    Parallel lines in 3D, coincident, skew and intersecting lines

    Upgrade to Plus

    Equations of a plane(Plus Only)

    Vector and scalar product forms of a plane, cartesian equation of a plane

    Upgrade to Plus

    Angles and intersections with planes(Plus Only)

    Intersection of a line and plane, angle between line and plane, intersection and angle between two planes, intersection of 3 planes

    Upgrade to Plus

    Differentiation

    8 concepts with notes

    Limits and Derivatives

    The concept (and basic properties) of limits and derivatives

    Start Lesson

    Differentiation rules

    Power rule, chain rule, product rule, quotient rule, derivatives of ex, ax, loga​(x), trigonometric, and inverse trigonometric functions

    Start Lesson

    Tangents and normals(Plus Only)

    Definitions of tangent and normal, finding tangent and normal lines to a function

    Upgrade to Plus

    Applications of the First Derivative(Plus Only)

    Increasing and decreasing intervals, stationary points (maxima and minima), and optimisation

    Upgrade to Plus

    Second Derivatives and Applications(Plus Only)

    Definition of the second derivative, concavity, inflexion points

    Upgrade to Plus

    n^th Derivative(Plus Only)

    Taking the nth derivative, inductive proofs with the nth derivative

    Upgrade to Plus

    Related Rates(Plus Only)

    Types of related rates, implicit differentiation

    Upgrade to Plus

    L'Hôpital's rule(Plus Only)

    A rule for evaluating limits of the form 0/0 or infinity/infinity

    Upgrade to Plus

    Integration

    5 concepts with notes

    Definite Integrals, Areas, and Basic Anti-Derivatives(Plus Only)

    Concept of an integral, areas with definite integrals, and basic anti-derivative solving skills

    Upgrade to Plus

    Anti-Derivative Rules

    Antiderivatives of polynomials, trigonometric, inverse trigonometric, exponential, and logarithmic functions

    Start Lesson

    Techniques of Integration(Plus Only)

    The reverse chain rule, integration by substitution, integration by parts, additional strategies

    Upgrade to Plus

    Kinematics(Plus Only)

    Computations involving distance, displacement, velocity, and acceleration

    Upgrade to Plus

    Volumes of Revolution

    Finding the volume of a solid revolved around a function or axis to create a 3D figure

    Start Lesson

    Differential Equations

    2 concepts with notes

    Solving Differential Equations

    An introduction to differential equations and how to solve them.

    Start Lesson

    Euler's Method

    Euler's method as a numerical method for finding particular solutions.

    Start Lesson

    Maclaurin

    2 concepts with notes

    Maclaurin Series Basics

    Learn to approximate complicated functions with polynomials and higher order derivatives.

    Start Lesson

    Operations on Maclaurin Series(Plus Only)

    We can find Maclaurin series for more complicated functions by combining multiple Maclaurin series.

    Upgrade to Plus

    Probability

    4 concepts with notes

    Probabilistic Events

    Theoretical and experimental probability, complementary events, expected number of outcomes, sample space

    Start Lesson

    Combined Events(Plus Only)

    Venn diagrams, intersection and union of events, conditional probability, independent events

    Upgrade to Plus

    Dependence(Plus Only)

    Tree diagrams, selection with/without replacement, dependence

    Upgrade to Plus

    Bayes' Theorem(Plus Only)

    Bayes' theorem with 2 and 3 events, sum of conditional probabilities

    Upgrade to Plus

    Descriptive Statistics

    6 concepts with notes

    Population & Data

    Understand the basics of population, data collection, and sampling.

    Start Lesson

    Measuring Center

    Learn different ways to measure the "center," or typical values, of a set of data: mean, median, and mode.

    Start Lesson

    Quartiles and Box & Whisker Plots(Plus Only)

    Learn the concept of dispersion, range, IQR, outliers, and box and whisker plots.

    Upgrade to Plus

    Standard Deviation and Variance(Plus Only)

    Learn about standard deviation and variance, which we use to measure how tightly or loosely clustered the data is around the mean.

    Upgrade to Plus

    Frequency Tables, Histograms and cumulative frequency diagrams(Plus Only)

    In this lesson, we learn about different ways to visualize data.

    Upgrade to Plus

    Linear Regression(Plus Only)

    Regressions of y on x, regressions of x on y, the correlation coefficient r, the rank correlation coefficient rs​, extrapolation and interpolation of data.

    Upgrade to Plus

    Distributions & Random Variables

    4 concepts with notes

    Discrete random variables

    Introduction and properties of random variables, probability distributions, expected value and variance, linear transformations of r.v.'s

    Start Lesson

    Binomial Distribution(Plus Only)

    Concept of the binomial distribution, binomial PDF and CDF, expectation and variance of binomial distribution

    Upgrade to Plus

    Normal Distribution(Plus Only)

    Introduction and definition of the normal distribution, standard deviations, normal and inverse normal calculations, z-values, normal standardization

    Upgrade to Plus

    Continuous random variables(Plus Only)

    Probability density, normalization, expectation and variance of c.r.v.'s. median and mode of c.r.v's

    Upgrade to Plus