Đáp án:
Câu `4:`
`a) (2m-3)(m+1)-(m-4)^2-m(m+7)`
`=2m^2+2m-3m-3-(m^2-8m+16)-m^2-7m`
`=2m^2-m-3-m^2+8m-16-m^2-7m`
`=(2m^2-m^2-m^2)-(m-8m+7m)-3-16`
`=-19`
`b) (x-2)^3+6(x-1)^2-(x+1)(x^2-x+1)`
`=x^3-6x^2+12x-8+6(x^2-2x+1)-(x^3+1)`
`=x^3-6x^2+12x-8+6x^2-12x+6-x^3-1`
`=(x^3-x^3)+(6x^2-6x^2)+(12x-12x)-8+6-1`
`=-3`
Câu `5:`
`a) 5x(x-1)=x-1 `
`=> 5x(x-1)-x+1=0`
`=> 5x(x-1)-(x-1)=0`
`=> (5x-1)(x-1)=0`
`=>` \(\left[ \begin{array}{l}5x-1=0\\x-1=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\dfrac{1}{5}\\x=1\end{array} \right.\)
`b) 2(x+5)-x^2-5x=0 `
`=> 2(x+5)-x(x+5)=0`
`=> (2-x)(x+5)=0`
`=>` \(\left[ \begin{array}{l}2-x=0\\x+5=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\)
`c) x^3-16x=0`
`=> x(x^2-16)=0`
`=> x(x-4)(x+4)=0`
`=>` \(\left[ \begin{array}{l}x=0\\x-4=0\\x+4=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=0\\x=4\\x=-4\end{array} \right.\)
`d) (2x-1)^2-(x+3)^2=0`
`=> (2x-1-x-3)(2x-1+x+3)=0`
`=> (x-4)(3x+2)=0`
`=>` \(\left[ \begin{array}{l}x-4=0\\3x+2=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=4\\x=-\dfrac{2}{3}\end{array} \right.\)
