a,45-15=-75-x
⇒x=-75-45+15
⇒x=-105
b,(6+x)(3-x)=0
⇒\(\left[ \begin{array}{l}6+x=0\\3-x=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-6\\x=3\end{array} \right.\)
c,x²-8x=0
⇒x(x-8)=0
⇒\(\left[ \begin{array}{l}x=0\\x=8\end{array} \right.\)
d,-3|x-7|=-21
⇒|x-7|=-21:(-3)
⇒|x-7|=7
⇒\(\left[ \begin{array}{l}x-7=7\\x-7=-7\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=14\\x=0\end{array} \right.\)
Chúc bạn học tốt nhé! ^^