Đáp án:
a,$(5x-10)(8-2x)=0$
⇔$5.(x-2).2.(4-x)=0$
⇔$(x-2).(4-x)=0$
⇔\(\left[ \begin{array}{l}x-2=0\\4-x=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=2\\x=4\end{array} \right.\)
b,$(x²+4)(7x-3)=0 (1)$
Vì $x²≥0$ nên $x²+4\neq0$
⇒(1)⇔$7x-3=0⇔x=\frac{3}{7}$