`@` `\text {Ans}`
`\downarrow`
`7)`
`2 \sqrt {1 - 2x} - 5 = 0`
`=> 2 \sqrt {1 - 2x} = 5`
`=> \sqrt {1 - 2x} = 5/2`
`=> 1 - 2x = (5/2)^2`
`=> 2x = 1 - (5/2)^2`
`=> 2x = 1 - 25/4`
`=> 2x = -21/4`
`=> x = -21/4 \div 2`
`=> x =-21/8`
Vậy, `x = -21/8`
`8)`
`(x^2 + 1)*(2x^2 - 3) = 0`
`=>`
`\text {TH1: } x^2 + 1 = 0`
`=> x^2 = 0 - 1`
`=> x^2 = -1 (\text {vô lý})`
Vậy, x không có gtr thỏa mãn
`\text {TH2: } 2x^2 - 3 = 0`
`=> 2x^2 = 0 + 3`
`=> 2x^2 = 3`
`=> x^2 = 3/2`
`=> x = +- \sqrt {3/2}`
Vậy, `x \in`\(\left\{-\sqrt{\dfrac{3}{2}};\sqrt{\dfrac{3}{2}}\right\}\)
2: =>2*căn 1-2x=5
=>căn 1-2x=5/2
=>1-2x=25/4
=>2x=1-25/4=-21/4
=>x=-21/8
8: =>2x^2-3=0 hoặc x^2+1=0(vô lý)
=>2x^2=3
=>x^2=3/2
=>\(x=\pm\dfrac{\sqrt{6}}{2}\)
9: =>|3/5*căn x-1/20|=3/4+1/5=19/20
=>3/5*căn x-1/20=-19/20 hoặc 3/5*căn x-1/20=19/20
=>3/5*căn x=-18/20(vô lý) hoặc 3/5*căn x=1
=>căn x=5/3
=>x=25/9
`9)`
`| 3/5 \sqrt {x} - 1/20| - 3/4 = 1/5`
`=> |3/5 \sqrt {x} - 1/20| = 1/5 + 3/4`
`=> |3/5 \sqrt {x} - 1/20| = 19/20`
`=>`\(\left[{}\begin{matrix}\dfrac{3}{5}\sqrt{x}-\dfrac{1}{20}=\dfrac{19}{20}\\\dfrac{3}{5}\sqrt{x}-\dfrac{1}{20}=-\dfrac{19}{20}\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}\dfrac{3}{5}\sqrt{x}=\dfrac{19}{20}+\dfrac{1}{20}\\\dfrac{3}{5}\sqrt{x}=-\dfrac{19}{20}+\dfrac{1}{20}\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}\dfrac{3}{5}\sqrt{x}=1\\\dfrac{3}{5}\sqrt{x}=-\dfrac{9}{10}\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}\sqrt{x}=\dfrac{5}{3}\\\sqrt{x}=-\dfrac{9}{10}\div\dfrac{3}{5}\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}x=\left(\dfrac{5}{3}\right)^2\\\sqrt{x}=-\dfrac{3}{2}\left(\text{vô lý}\right)\end{matrix}\right.\)
Vậy, `x = 25/9.`
