Question

Cho biểu thức:

A= (\(2-\dfrac{\sqrt{x}-1}{2\sqrt{x}-3}\)) : (\(\dfrac{6\sqrt{x}+1}{2x-\sqrt{x}-3}+\dfrac{\sqrt{x}}{\sqrt{x}+1}\))

a) Rút gọn A

b) Tính A khi x = \(\dfrac{3-2\sqrt{2}}{4}\)

Answer 1

a: \(A=\dfrac{4\sqrt{x}-6-\sqrt{x}+1}{2\sqrt{x}-3}:\left(\dfrac{6\sqrt{x}+1}{\left(2\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}+\dfrac{\sqrt{x}}{\sqrt{x}+1}\right)\)

\(=\dfrac{3\sqrt{x}-5}{2\sqrt{x}-3}:\dfrac{6\sqrt{x}+1+2x-3\sqrt{x}}{\left(2\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3\sqrt{x}-5}{\left(2\sqrt{x}-3\right)}\cdot\dfrac{\left(2\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}{\left(2\sqrt{x}+1\right)\left(\sqrt{x}+1\right)}=\dfrac{3\sqrt{x}-5}{2\sqrt{x}+1}\)

b: Thay \(x=\dfrac{\left(\sqrt{2}-1\right)^2}{4}\) vào A, ta được:

\(A=\left(3\cdot\dfrac{\sqrt{2}-1}{2}-5\right):\left(2\cdot\dfrac{\sqrt{2}-1}{2}+1\right)\)

\(=\dfrac{3\sqrt{2}-3-10}{2}:\dfrac{2\sqrt{2}-2+2}{2}\)

\(=\dfrac{3\sqrt{2}-13}{2\sqrt{2}}=\dfrac{6-13\sqrt{2}}{4}\)