Đáp án:
`a)A=(\sqrt(20)-sqrt(45)+3sqrt5)*sqrt5`
`=(2sqrt5-3sqrt5+3sqrt5)*sqrt5`
`=2sqrt5*sqrt5=10`
`B=(x+1-2sqrtx)/(sqrtx-1)+(x+sqrtx)/(sqrtx+1)(x>=0,x ne 1)`
`=(sqrtx-1)^2/(sqrtx-1)+(sqrtx(sqrtx+1))/(sqrtx+1)`
`=sqrtx-1+sqrtx`
`=2sqrtx-1`
`b)A=B`
`<=>2sqrtx-1=5`
`<=>2sqrtx=6`
`<=>sqrtx=3`
`<=>x=9(tmđk)`