Rút gọn biểu thức: (A = left( {frac{{x - sqrt x + 2}}{{x - sqrt x - 2}} - frac{x}{{x - 2sqrt x }}} right):frac{{1 - sqrt x }}{{2 - sqrt x }}) với (x > 0,x ne 1,x ne 4.)
Giải chi tiết:
ĐKXĐ: (x > 0,x ne 1,x ne 4.)
(begin{array}{l}A = left( {frac{{x - sqrt x + 2}}{{x - sqrt x - 2}} - frac{x}{{x - 2sqrt x }}} right):frac{{1 - sqrt x }}{{2 - sqrt x }} = left( {frac{{x - sqrt x + 2}}{{left( {sqrt x - 2} right)left( {sqrt x + 1} right)}} - frac{{sqrt x .sqrt x }}{{sqrt x .left( {sqrt x - 2} right)}}} right).frac{{sqrt x - 2}}{{sqrt x - 1}} = left( {frac{{x - sqrt x + 2}}{{left( {sqrt x - 2} right)left( {sqrt x + 1} right)}} - frac{{sqrt x left( {sqrt x + 1} right)}}{{left( {sqrt x - 2} right)left( {sqrt x + 1} right)}}} right).frac{{sqrt x - 2}}{{sqrt x - 1}} = frac{{x - sqrt x + 2 - left( {x + sqrt x } right)}}{{left( {sqrt x - 2} right)left( {sqrt x + 1} right)}}.frac{{sqrt x - 2}}{{sqrt x - 1}} = frac{{ - 2left( {sqrt x - 1} right)}}{{left( {sqrt x + 1} right)left( {sqrt x - 1} right)}} = frac{{ - 2}}{{sqrt x + 1}}.end{array})
Vậy (A = frac{{ - 2}}{{sqrt x + 1}}).()
Chọn A.