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Algebra Level 2

Find the largest solution of 4 x 3 + 10 4 x 3 = 7 \sqrt{4x-3}+\frac{10}{\sqrt{4x-3}}=7 .


The answer is 7.

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1 solution

Patrick Prochazka
Jul 16, 2015

Let u = 4 x 3 u= \sqrt{4x-3} . Thus, our equation becomes: u + 10 u = 7 u + \frac{10}{u} = 7 , or u 2 7 u + 10 u^2 - 7u + 10 . Solving this quadratic gives u = 2 u=2 or u = 5 u=5 .

If u = 2 u=2 , then 4 x 3 = 2 \sqrt{4x-3} = 2 , or x = 7 4 x = \frac{7}{4} .

If u = 5 u=5 , then 4 x 3 = 5 \sqrt{4x-3} = 5 , or x = 7 x = 7 .

Since the larger of these two solutions, is 7 7 , our answer is 7 \fbox{7} .

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