Đáp án:
`a)A=2sqrt{20}-(5-sqrt5)/(sqrt5-1)-10sqrt{1/5}`
`A=2sqrt{4.5}-(sqrt5(sqrt5-1))/(sqrt5-1)-2.5.sqrt{1/5}`
`A=4sqrt5-sqrt5-2sqrt5`
`A=sqrt5`
`b)B=(x+1)/(sqrtx-1)-(2x+2sqrtx)/(x-1)(x>0,x ne 1)`
`B=(x+1)/(sqrtx-1)-(2sqrtx(sqrtx+1))/((sqrtx-1)(sqrtx+1))`
`B=(x+1)/(sqrtx-1)-(2sqrtx)/(sqrtx-1)`
`B=(x-2sqrtx+1)/(sqrtx-1)`
`B=(sqrtx-1)^2/(sqrtx-1)`
`B=sqrtx-1`
`c)B=A^2`
`<=>sqrtx-1=(sqrt5)^2=5`
`<=>sqrtx=6`
`<=>x=36(tmđk)`
Vậy `x=36` thì `B=A^2`.
