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Y and A Tutoring Paper 2 with Answers and Hints · Q4

Paper 2Logic & proof

Consider the following incorrect attempt at a proof, given that aa and bb are real numbers such that a=ba=b. On which line does the first mistake occur?

Aa2=aba^2=ab
Ba2−b2=ab−b2a^2-b^2=ab-b^2
C(a−b)(a+b)=b(a−b)(a-b)(a+b)=b(a-b)
Da+b=ba+b=b
E2b=b2b=b
F2=12=1

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