Bài 1:
1: 2155-(174+2155)+(-68+174)
=2155-174-2155-68+174
=(2155-2155)+(-174+174)-68
=0+0-68
=-68
2: \(-25\cdot72+25\cdot21-49\cdot25\)
\(=25\left(-72+21-49\right)\)
\(=25\cdot\left(-100\right)=-2500\)
3: \(35\cdot\left(14-23\right)-23\cdot\left(14-35\right)\)
\(=35\cdot14-35\cdot23-23\cdot14+23\cdot35\)
\(=35\cdot14-23\cdot14=14\cdot12=168\)
4: \(8154-\left(674+8154\right)+\left(-98+674\right)\)
=8154-674-8154-98+674
=(8154-8154)+(674-674)-98
=0+0-98
=-98
5: \(-25\cdot21+25\cdot72+49\cdot25\)
\(=25\left(-21+72+49\right)\)
\(=25\cdot100=2500\)
6: \(27\cdot\left(13-16\right)-16\left(13-27\right)\)
\(=27\cdot13-27\cdot16-16\cdot13+16\cdot27\)
\(=27\cdot13-16\cdot13=13\cdot\left(27-16\right)=13\cdot11=143\)
7: -1911-(1234-1911)
=-1911-1234+1911
=-1234
8: \(156\cdot72+28\cdot156\)
\(=156\cdot\left(72+28\right)\)
\(=156\cdot100=15600\)
Bài 2:
1: x-2=-6
=>x=-6+2
=>x=-4
2: -5x-(-3)=13
=>-5x+3=13
=>-5x=13-3=10
=>x=-2
9: |x-3|-7=13
=>|x-3|=7+13=20
=>\(\left[\begin{array}{l}x-3=20\\ x-3=-20\end{array}\right.\Rightarrow\left[\begin{array}{l}x=23\\ x=-17\end{array}\right.\)
10: \(72-3\left|x+1\right|=9\)
=>3|x+1|=72-9=63
=>|x+1|=21
=>\(\left[\begin{array}{l}x+1=21\\ x+1=-21\end{array}\right.\Rightarrow\left[\begin{array}{l}x=20\\ x=-22\end{array}\right.\)
16: (7-x)(x+19)=0
=>\(\left[\begin{array}{l}7-x=0\\ x+19=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=7\\ x=-19\end{array}\right.\)
