Tìm x biết : a. (5x-4)^2 – 49x^2 = 0 b. x^2 +3x-10 =0

Đáp án:

a)\(\left[ \begin{array}{l}x=-2\\x=\dfrac{1}{3}\end{array} \right.\) 

b)\(\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\) 

Giải thích các bước giải:

 $a)(5x-4)^2-49x^2=0$

$⇔(5x-4-7x).(5x-4+7x)=0$

$⇔(-2x-4).(12x-4)=0$

⇔\(\left[ \begin{array}{l}-2x-4=0\\12x-4=0\end{array} \right.\) 

⇔\(\left[ \begin{array}{l}x=-2\\x=\dfrac{1}{3}\end{array} \right.\) 

$b)x^2+3x-10=0$

$⇔x^2-2x+5x-10=0$

$⇔x.(x-2)+5.(x-2)=0$

$⇔(x-2).(x+5)=0$

\(\left[ \begin{array}{l}x-2=0\\x+5=0\end{array} \right.\) 

\(\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\)