Discussion of Question with ID = 007 under Square-and-Cube-Roots

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Question

What is the value of $√{(13 - 5√5) × (13 + 5√5)}$?

A

$√44$.

B

$√25$.

C

$√5$.

D

$√65$.

Soln.
Ans: a

By inspection, we can easily see that the formula (a - b) × (a + b) can be used to simplify like this: $√{(13)^2 - (5√5)^2}$, which is same as $√{169 - (5^2 × 5)}$, which is same as $√{169 - 125}$ = $√44$.


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