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  • Perplex

    Trig equations & identities (Lesson 2/6)

    The Unit Circle

    1 / 25

    Discussion

    Imagine we have a circle centered about the origin O(0,0) with radius 1, and we place a point P on its circumference such that the line (OP) forms an acute angle of 30° with the x-axis:

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    (a)

    Find the coordinates of P.

    Solution:

    The hypotenuse of the triangle is the radius of the circle, which is 1. The triangle is placed so that its hypotenuse makes a 30∘ angle with the x-axis, starting from the origin.


    To find the coordinates where the triangle (hypotenuse) meets the circle, we use the definitions of sine and cosine for a right triangle:

    sinθ=hypotenuseopposite​cosθ=hypotenuseadjacent​

    These are the SOH and CAH formulas.

    Since the hypotenuse is 1, the coordinates of the point on the circle at a 30∘ angle from the x-axis are:

    (cos(30∘),sin(30∘))


    Evaluate cos(30∘) and sin(30∘) using a calculator:

    cos(30∘)sin(30°)​≈0.866(which is actually 2√3​)=0.5​

    So, the intersection point is:

    (0.866,0.5)