`\text{ Bạn xem xong đánh giá cho mk nhé :33}`
`\text{Bài 17:}`
`@a)\frac{\sqrt{t}-3}{\sqrt{2t}+t}=2, Đk {(t-3>=0),(2t+t>0):}<=>{(t>=3),(t> -1/2):}`
`<=>\sqrt{t}-3=2\sqrt{2t+1}`
`<=>(\sqrt{t-3})^2=(2\sqrt{2t+1})^2`
`<=>t-3=4(2t+1)`
`<=>t-3=8t+4<=>-7t=7=>t=-1(l)`
`@b)\sqrt{25t^2-9}=2\sqrt{5t-3}`
`đk{(25t^2-9>=0),(5t-3>=0):}<=>{(t>=3/5 nn t <=\frac{-3}{5}),(t>=3/5):}`
`<=>(\sqrt{25t^2-9})^2=(2\sqrt{5t-3})^2`
`<=>25t^2-9=4(5t-3)`
`<=>25t^2-20t+3=0`
`\Delta'=(-20/2)^2-25.3=25`
`=>\sqrt{\Delta'}=5`
`=>{(t=\frac{10-5}{25}=1/5(l)),(t=\frac{10+5}{25}=3/5(n)):}`
`\text{Bài 18:}`
`@a)\sqrt{-2x^2+6}=x-1`
`đk-2x^2+6>=0<=>x^2<=3`
`<=>-\sqrt{3}<=x<=\sqrt{3}`
`<=>(\sqrt{-2x+6})^2=(x-1)^2`
`<=>-3x^2+6=x^2-2x+1`
`<=>-3x^2+2x+5=0`
`\Delta'=(1)^2+3.6=16=>\sqrt{Delta'}=4`
`=>{(x=\frac{-1-4}{-3}=5/3(n)),(x=\frac{-1+4}{-3}=-1(n)):}`
`@b)\sqrt{t-5}+\sqrt{4t-20}-1/5\sqrt{9t-45}=3`
`đk` `t-5>=0=>t>=5`
`<=>\sqrt{t-5}+\sqrt{4(t-5)}-1/5\sqrt{9(t-5)}=3`
`Đặt` `x=\sqrt{t-5}`
`<=>x+2.x-1/5 .3.x=3`
`<=>12/5 x=3=>x= 5/4`
`<=>\sqrt{t-5}=5/4<=>t-5=25/16`
`=>t=105/16`
