Đáp án:+Giải thích các bước giải:

`B=(2\sqrtx)/(\sqrtx+3)+\sqrtx/(\sqrtx-3)-(3x+3)/(x-9) (x >=0; x \ne 9)`

`=(2\sqrtx(\sqrtx-3))/((\sqrtx+3)(\sqrtx-3))+(\sqrtx(\sqrtx+3))/((\sqrtx+3)(\sqrtx-3))-(3x+3)/((\sqrtx+3)(\sqrtx-3))`

`=(2\sqrtx(\sqrtx-3)+\sqrtx(\sqrtx+3)-(3x+3))/((\sqrtx+3)(\sqrtx-3))`

`=(2x-6\sqrtx+x+3\sqrtx-3x-3)/((\sqrtx+3)(\sqrtx-3))`

`=(-3\sqrtx-3)/((\sqrtx+3)(\sqrtx-3))`

_______________________

`C=4/(x-1)+(\sqrtx+3)/(\sqrtx+1)+5/(1-\sqrtx)(x>=0; x \ne 1)`

`=4/((\sqrtx+1)(\sqrtx-1))+((\sqrtx+3)(\sqrtx-1))/((\sqrtx+1)(\sqrtx-1))-(5(\sqrtx+1))/((\sqrtx+1)(\sqrtx-1))`

`=(4+(\sqrtx+3)(\sqrtx-1)-5(\sqrtx+1))/((\sqrtx+1)(\sqrtx-1))`

`=(4+x+2\sqrtx-3-5\sqrtx-5)/((\sqrtx+1)(\sqrtx-1))`

`=(x-3\sqrtx-4)/((\sqrtx+1)(\sqrtx-1))`

`=(x+\sqrtx-4\sqrtx-4)/((\sqrtx+1)(\sqrtx-1))`

`=(\sqrtx(\sqrtx+1)-4(\sqrtx+1))/((\sqrtx+1)(\sqrtx-1))`

`=((\sqrtx+1)(\sqrtx-4))/((\sqrtx+1)(\sqrtx-1))`

`=(\sqrtx-4)/(\sqrtx-1)`

______________________

`D=\sqrtx/(\sqrtx+6)+1/(\sqrtx-6)+(17\sqrtx+30)/(x-36) (x >=; x\ne 36)`

`=(\sqrtx(\sqrtx-6))/((\sqrtx+6)(\sqrtx-6))+(\sqrtx+6)/((\sqrtx+6)(\sqrtx-6))+(17\sqrtx+30)/((\sqrtx+6)(\sqrtx-6))`

`=(\sqrtx(\sqrtx-6)+\sqrtx+6+17\sqrtx+30)/((\sqrtx+6)(\sqrtx-6))`

`=(x-6\sqrtx+18\sqrtx+36)/((\sqrtx+6)(\sqrtx-6))`

`=(x+12\sqrtx+36)/((\sqrtx+6)(\sqrtx-6))`

`=(\sqrtx+6)^2/((\sqrtx+6)(\sqrtx-6))`

`=(\sqrtx+6)/(\sqrtx-6)`

________________

`E=x/(x-16)-2/(\sqrtx-4)-2/(\sqrtx+4)(x>=0;x\ne 16)`

`=x/((\sqrtx+4)(\sqrtx-4))-(2(\sqrtx+4))/((\sqrtx+4)(\sqrtx-4))-(2(\sqrtx-4))/((\sqrtx+4)(\sqrtx-4))`

`=(x-2(\sqrtx+4)-2(\sqrtx-4))/((\sqrtx+4)(\sqrtx-4))`

`=(x-2\sqrtx-8-2\sqrtx+8)/((\sqrtx+4)(\sqrtx-4))`

`=(x-4\sqrtx)/((\sqrtx+4)(\sqrtx-4))`

`=(\sqrtx(\sqrtx-4))/((\sqrtx+4)(\sqrtx-4))`

`=\sqrtx/(\sqrtx+4)`