Equal to what?

Algebra Level 3

7 + 4 3 2 = ? \large\sqrt{\dfrac{7+ 4\sqrt{3}}{2}} = ?

2 + 6 2 \frac {\sqrt{2} +\sqrt{6}}2 2 + 6 \sqrt{2} + \sqrt{6} 2 2 + 6 2 \frac {2\sqrt{2} +\sqrt{6}}2 3 + 2 4 \frac {\sqrt{3} + 2}4

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1 solution

Philip Lee
Aug 14, 2017

Express the contents of the square root in the form of a 2 + 2 a b + b 2 a^2+2ab+b^2 so that it can be factorised to ( a + b ) 2 \left(a+b\right)^2 .

7 + 4 3 2 = 4 + 4 3 + 3 3 = ( 2 + 3 ) 2 2 = 2 + 3 2 \begin{aligned} \sqrt{\frac{7+4\sqrt{3}}{2}} &= \sqrt{\frac{4+4\sqrt{3}+3}{3}} \\ &= \sqrt{\frac{\left(2+\sqrt{3}\right)^2}{2}} \\ &= \frac{2+\sqrt{3}}{\sqrt{2}} \end{aligned}

Then rationalise the denominator to get 2 2 + 6 2 \frac{2\sqrt{2}+\sqrt{6}}{2} _\square

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