Question

Find the value of $(\sqrt{7}+\sqrt{7})(\sqrt{7}-\sqrt{7})$.

• A. 0.0
• B. 1
• C. 2
• D. 7

Answer 1

The correct option is A 0.0

A common tendency to solve this question is to apply the algebraic identity $(a^2-b^2)=(a+b)(a-b)$. But by observation, we can see that $(\sqrt{7}-\sqrt{7})$, which is one of the factors, will result in 0, thus making the final value of the whole expression as 0 i.e.
$(\sqrt{7}+\sqrt{7})(\sqrt{7}-\sqrt{7})$
$=(\sqrt{7}+\sqrt{7})\times \left(0\right)$
$=0$