2 câu trả lời
Giải: $\frac{6}{\sqrt{11}+3}-\frac{6}{\sqrt{11}-3}$
$=\frac{6(\sqrt{11}-3)}{(\sqrt{11}+3)(\sqrt{11}-3)}-\frac{6(\sqrt{11}+3)}{(\sqrt{11}-3)(\sqrt{11}+3)}$
$=\frac{(6\sqrt{11}-18)-(6\sqrt{11}+18)}{11-9}$
$=\frac{6\sqrt{11}-18-6\sqrt{11}-18}{2}$
$=\frac{-36}{2}$
$=-18$
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Đáp án + Giải thích các bước giải:
`6/( sqrt {11} + 3 ) - 6/( sqrt {11} - 3 )`
`= ( 6 ( sqrt {11} - 3 ) )/( ( sqrt {11} + 3 )( sqrt {11} - 3 ) ) - ( 6 ( sqrt {11} + 3 ) )/( ( sqrt {11} + 3 )( sqrt {11} - 3 ) )`
`= ( 6 ( sqrt {11} - 3 ) )/( 11 - 9 ) - ( 6 ( sqrt {11} + 3 ) )/( 11 - 9 )`
`= ( 6 ( sqrt {11} - 3 ) )/2 - ( 6 ( sqrt {11} + 3 ) )/2`
`= 3 ( sqrt {11} - 3 ) - 3 ( sqrt {11} + 3 )`
`= 3 sqrt {11} - 9 - 3 sqrt {11} - 9`
`= -18`