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  • Perplex

    Proof and Reasoning (Lesson 1/1)

    Proof by deduction

    1 / 9

    Discussion

    Consider the sum ​1+3+5+⋯+(2n−1).


    This is what we call a conjecture - basically an informed guess about some pattern that we see sometimes holds.

    (a)

    Evaluate the sum in the case ​n=3,4,5.

    Solution:

    Compute directly by adding the first few odd numbers.

    • For ​n=3:

      ​
      1+3+5=9
      ​


    • For ​n=4:

      ​
      1+3+5+7=16
      ​


    • For ​n=5:

      ​
      1+3+5+7+9=25
      ​


    So the sums are ​9,16,25​ respectively.