bài 1
a)\(15+\left(3-x\right)=-10\)
\(3-x=-10-15\)
\(3-x=-25\)
\(x=3-\left(-25\right)\)
\(x=28\)
b)\(11-\left(-53+x\right)=97\)
\(-53+x=11-97\)
\(-53+x=-86\)
\(x=-86-\left(-53\right)\)
\(x=-33\)
c)\(5x-\left(-25\right)=35\)
\(5x+25=35\)
\(5x=35-25\)
\(5x=10\)
\(x=10:5\)
\(x=2\)
bài 2
\(-50\le x< 51\)
Mà \(x\in Z\)
\(\Rightarrow x\in\left\{-50;-49;...;50\right\}\)
Tổng các số nguyên x là:
\(-50+\left(-49\right)+...+50\)
\(=\left(-50+50\right)+\left(-49+49\right)+...+\left(-1+1\right)+0\)
\(=0+0+...+0+0\)
\(=0\)
bài 3:
Ta có:\(n-7\inƯ\left(5\right)=\left\{\pm1;\pm5\right\}\)
Ta có bảng sau:
| n - 7 | 1 | -1 | 5 | -5 |
| n | 8 | 6 | 12 | 2 |
Vậy\(n\in\left\{8;6;12;2\right\}\)
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