Đáp án + Giải thích các bước giải:
a)
Thay `x=4` vào `B` ta có:
`B=(4-\sqrt4)/(2\sqrt4+1)=(4-2)/(2.2+1)=2/(4+1)=2/5`
b)
`M=A.B`
`=>M=(1/(\sqrtx-1)+(\sqrtx)/(x-1)).(x-\sqrtx)/(2\sqrtx+1)(x\ge0;x\ne1)`
`=>M=((\sqrtx+1)/(x-1)+(\sqrtx)/(x-1)).(x-\sqrtx)/(2\sqrtx+1)`
`=>M=(\sqrtx+1+\sqrtx)/(x-1).(\sqrtx(\sqrtx-1))/(2\sqrtx+1)`
`=>M=((2\sqrtx+1).\sqrtx(\sqrtx-1))/((\sqrtx-1)(\sqrtx+1)(2\sqrtx+1))`
`=>M=(\sqrtx)/(\sqrtx+1)`
