alleryWhich identity is correct?
A$(a+b)^2-(a-b)^2=2ab$
B$(a+b)^2+(a-b)^2=2ab$
C$(a+b)^2-(a-b)^2=4ab$
D$(a+b)^2+(a-b)^2=4ab$
Answer & Solution
Correct answer: C. $(a+b)^2-(a-b)^2=4ab$
**Expand both squares:** $(a+b)^2=a^2+2ab+b^2$ and $(a-b)^2=a^2-2ab+b^2$.
Subtracting gives $4ab$.
The sum, not the difference, equals $2(a^2+b^2)$, so the other options are incorrect.
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