Bài giải
a, \(217-7\left(x-1\right)=100\)
\(7\left(x-1\right)=217-100\)
\(7\left(x-1\right)=117\)
\(x-1=\frac{117}{7}\)
\(x=\frac{117}{7}+1\)
\(x=\frac{166}{7}\)
b, \(2\cdot\left|x\right|-72=6^2-8\)
\(2\cdot\left|x\right|-72=36-8\)
\(2\cdot\left|x\right|-72=28\)
\(2\cdot\left|x\right|=28+72\)
\(2\cdot\left|x\right|=100\)
\(\left|x\right|=100\text{ : }2\)
\(\left|x\right|=50\)
\(\Rightarrow\text{ }x\in\left\{\pm50\right\}\)