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What is the value of \(\frac{1}{2}\sqrt{21+12√3}-√3\) ?

(A) \(\frac{1}{2}\)

(B) \(\frac{2}{3}\)

(C) \(\frac{3}{2}\)

(D) \(\frac{6}{7}\)

(E) \(\frac{7}{4}\)

Fastest Method

: APPROXIMATION

\(\frac{1}{2}\sqrt{21+12√3}-√3=\frac{1}{2}\sqrt{21+12*1.7}-√3 ≈ \frac{1}{2}\sqrt{41}-1.7 = \frac{1}{2}*6.4-1.7 = 3.2-1.7 = 1.5\)

Answer: Option C
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­↧↧↧ Detailed Video Solution to the Problem Series ↧↧↧



We need to simplify \(\frac{1}{2}\sqrt{21+12√3}-√3\)

In order to solve these kind of problems involving nested square roots, we need to simplify the terms inside the bigger square root to convert them to a perfect square

=> We need to write 21+12√3 as \((a+b)^2\)


Now, we will try to write 21 as \(a^2 + b^2\) and 12√3 as 2*a*b
=> 12√3 = 2 * 2√3 * 3
And 21 = \((2√3)^2 + 3^2\) = 4*3 + 9 = 12 + 9

=> \(21 + 12√3\) = \((2√3 + 3)^2\)
=> \(\frac{1}{2}\sqrt{21+12√3}-√3\) = \(\frac{1}{2}\sqrt{(2√3 + 3)^2}-√3\)
= \(\frac{1}{2}(2√3 + 3) - √3\) = √3 + 3/2 - √3 = 3/2

So, Answer will be C
Hope it helps!

Watch the following video to MASTER Roots

­
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