Đáp án:
`d) 4x^2-25-(2x-5)(2x+7)=0`
`<=> (2x-5)(2x+5)-(2x-5)(2x+7)=0`
`<=> (2x-5)(2x+5-2x-7)=0`
`<=> -2(2x-5)=0`
`<=> 2x-5=0`
`<=>x=5/2`
`e) x^2+4x+3=0`
`<=> x^2+x+3x+3=0`
`<=> x(x+1)+3(x+1)=0`
`<=> (x+1)(x+3)=0`
`<=>`\(\left[ \begin{array}{l}x+1=0\\x+3=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=-1\\x=-3\end{array} \right.\)
`f) 4x^2+4x-3=0`
`<=> 4x^2+4x+1-4=0`
`<=> (2x+1)^2-4=0`
`<=> (2x+1-2)(2x+1+2)=0`
`<=> (2x-1)(2x+3)=0`
`<=>`\(\left[ \begin{array}{l}2x-1=0\\2x+3=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=1/2\\x=-3/2\end{array} \right.\)
`g) x^2-x=12`
`<=> x^2-x-12=0`
`<=> x^2+3x-4x-12=0`
`<=> x(x+3)-4(x+3)=0`
`<=> (x+3)(x-4)=0`
`<=>`\(\left[ \begin{array}{l}x+3=0\\x-4=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-3\\x=4\end{array} \right.\)
