Bài 1:
a) -56.|-51|-54.|+51|
=-56.51-54.51
=51.(-56-54)
=51.110
=5610
b) 12.(-5)²-6.(-15)
=12.25-6.(-15)
=2.6.25+6.15
=6.(2.25+15)
=6.(50+15)
=6.65
=390
Bài 2:
a) (4x+12) (1-x)=0
\(\left[ \begin{array}{l}4x+12=0\\1-x=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}4x=-12\\x=1\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=-12:4\\x=1\end{array} \right.\)(=) \(\left[ \begin{array}{l}x=-3\\x=1\end{array} \right.\)
b) |2x+5|-47=-8
|2x+5|=-8+47
|2x+5|=39
2x+5=±39
Trường hợp 1: 2x+5=39
2x=39-5
2x=34
x=34:2
x=17
Trường hợp 2: 2x+5=-39
2x=-39-5
2x=-44
x=-44:2
x=-22
