Question

If x+y = 85 and x-y =9 then what is the difference of their squares?
a. 765
b.845
C.565
d.645

Answer 1

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Answer 2

${x}^{2} - {y}^{2} = (x + y)(x - y) \\ {x}^{2} - {y}^{2} = 85 \times 9 \\ {x}^{2} - {y}^{2} = 765$
answer is A