Đáp án:
`B=1`
Giải thích các bước giải:
`B = (x/(x+3\sqrtx) + 1/(\sqrtx+3) ) : (1 - 2/\sqrtx + 6/(x+3\sqrtx)) (x>0)`
`=(x/(\sqrtx(\sqrtx+3))+1/(\sqrtx+3)):(1-2/\sqrtx+6/(\sqrtx(\sqrtx+3)))`
`=(\sqrtx/(\sqrtx+3)+1/(\sqrtx+3)):(\sqrtx(\sqrtx+3)-2(\sqrtx+3)+6)/(\sqrtx(\sqrtx+3)`
`=(\sqrtx+1)/(\sqrtx+3):(x+3\sqrtx-2\sqrtx-6+6)/(\sqrtx(\sqrtx+3))`
`=(\sqrtx+1)/(\sqrtx+3) : (x+\sqrtx)/(\sqrtx(\sqrtx+3))`
`=(\sqrtx+1)/(\sqrtx+3).(\sqrtx(\sqrtx+3))/(\sqrtx(\sqrtx+1))=1`
