Bài 7:
a: x:(-2)=9
=>\(x=-2\cdot9=-18\)
b: 4x+(-8)=24
=>4x-8=24
=>4x=8+24=32
=>\(x=\frac{32}{4}=8\)
c: \(\left(3-x\right)\left(x+7\right)=0\)
=>\(\left[\begin{array}{l}3-x=0\\ x+7=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=3\\ x=-7\end{array}\right.\)
d: \(-15:x=3\)
=>x=-15/3=-5
e: \(-3x+8=-7\)
=>-3x=-7-8
=>-3x=-15
=>x=5
f: (x-6)(7-x)=0
=>\(\left[\begin{array}{l}x-6=0\\ 7-x=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=6\\ x=7\end{array}\right.\)
Bài 6:
a: 13-18-(-42)-15
=-5-15+42
=-20+42
=22
b: \(369-4\cdot\left\lbrack\left(-5\right)+4\left(-8\right)\right\rbrack\)
\(=369-4\cdot\left\lbrack-5-32\right\rbrack=369+4\cdot37\)
=369+148
=517
c: \(\left(-8\right)^3:\left(-8\right)^2+8=-8+8=0\)
d: \(\left(-12\right)\cdot\left(-13\right)+13\cdot\left(-29\right)\)
\(=12\cdot13+13\cdot\left(-29\right)\)
\(=13\left(-29+12\right)=13\cdot\left(-17\right)=-221\)
