Toán Lớp 9: Giup mình với ạ!!!!
Rút gọn: $x\sqrt[]{\frac{5}{-x} }$ – $\frac{\sqrt[]{28x^{6} } }{\sqrt[]{7x^{4} } }$ (x<0)
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Toán Lớp 9: Giup mình với ạ!!!!
Rút gọn: $x\sqrt[]{\frac{5}{-x} }$ – $\frac{\sqrt[]{28x^{6} } }{\sqrt[]{7x^{4} } }$ (x<0)
Comments ( 1 )
=x\sqrt{\frac{5}{-x}}-\sqrt{\frac{28x^6}{7x^4}}
=x\sqrt{\frac{5}{-x}}-\sqrt{\frac{28}{7}}.\sqrt{\frac{x^6}{x^4}}
=x\sqrt{\frac{5}{-x}}-4.\sqrt{\frac{(x^3)^2}{(x^2)^2}}
=\sqrt{\frac{5x^2}{-x}}-4.|\frac{x^3}{x^2}|
=\sqrt{-5x}-4.|\frac{x^3}{x^2}|
Vì x^2>0;x<0<=>x^3<0=>\frac{x^3}{x^2}<0
=\sqrt{-5x}-4.-\frac{x^3}{x^2}
=\sqrt{-5x}+4x