B4
\(a,=\left(-278-22\right)+\left(109+91\right)=-300+200=-100\)
\(b,=\left(-23+123\right)+\left(289-689\right)=100+\left(-400\right)=-300\)
\(c,=\left(-23+123\right)+\left(-24+124\right)+\left(-25+125\right)\\ =100+100+100=300\)
\(d,=800+1267-987-67+1987\\ =\left(1267-67\right)+\left(1987-987\right)+800\\ =1200+1000+800=3000\)
B5
\(a,=12\cdot\left[\left(-47\right)+\left(-19\right)\right]+\left(-66\right)\cdot88\\ =12\cdot\left(-66\right)+\left(-66\right).88\\ =-66\cdot\left(12+88\right)=-66\cdot100\\ =-6600\)
\(b,=-135\cdot29+13\cdot\left(-135\right)+42\cdot\left(-65\right)\\ =-135\cdot\left(29+13\right)+42.\left(-65\right)\\ =-135\cdot42+42.\left(-65\right)\\ =42\cdot\left[\left(-135\right)+\left(-65\right)\right]=42\cdot\left(-200\right)\\ =-8400\)
lần sau 1 lần 1 bài nha, chia đôi cho khỏi bị mất phần thôi
B6
\(a,\rightarrow\left(x-1\right)^2=1^2\\ \rightarrow x-1=1\\ x=1+1\\ x=2\)
\(b,\rightarrow7^{2x-6}=7^2\\ \rightarrow2x-6=2\\ 2x=2+6=8\\ x=8:2\\ x=4\)
\(c,\rightarrow13\cdot x=565-370\\ 13\cdot x=195\\ x=195:13\\ x=15\)
\(d,\rightarrow\left(135-7x\right):9=105-97=8\\ 135-7x=8.9=72\\ 7x=135-72=63\\ x=63:7\\ x=9\)
\(e,\rightarrow275-\left(113+x\right)=158-63=95\\ 113+x=275-95=180\\ x=180+113\\ x=67\)
\(f,\rightarrow3\cdot\left(x+2\right):7=120:4=30\\ 3\cdot\left(x+2\right)=30\cdot7=210\\ x+2=210:3=70\\ x=70-2\\ x=68\)
