Đáp án:
Giải thích các bước giải:
c)3x.(x-2) -x² +2x =0
⇔3x² -6x -x² +2x=0
⇔2x² -4x =0
⇔2x.(x-2) =0
⇔\(\left[ \begin{array}{l}x=0\\x-2=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0\\x =2\end{array} \right.\)
d)x+5 =2.(x+5)²
⇔(x+5) -2.(x+5)²=0
⇔(x+5).( 1-2.(x+5) =0
⇔(x+5).(1 -2x -10)=0
⇔(x+5).(-2x -9)=0
⇔\(\left[ \begin{array}{l}x+5=0\\-2x-9=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x =-5\\x =-9/2\end{array} \right.\)
e)4x² -25 -(2x -5).(2x+7) =0
⇔4x² -25 -(4x² +4x -35)=0
⇔4x² -25 -4x² -4x +35 =0
⇔-4x +10=0
⇔4x =10
⇔ x=$\frac{5}{2}$
f) x² +x -12=0
⇔x² -4x +3x -12=0
⇔x.(x-4) +3.(x-4)=0
⇔(x-4).(x+3)=0
⇔\(\left[ \begin{array}{l}x-4=0\\x+3=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=4\\x =-3\end{array} \right.\)
