[tex]General\ equation\ for\ line\ in\ slope\ intercept\ form:\\\\y=ax+b\\\\To\ find\ a\ and\ b\ substitude\ points\ (-2,7),\ (1,-2)\ into\ equation\\\\ \left \{ {{7=-2a+b} \atop {-2=a+b\ \ |:-1}} \right.
\\\\ \left \{ {{7=-2a+b} \atop {2=-a-b}} \right. \\+-----\\\\9=-3a\ \ \ |:-3\\a=-3\\\\-2=-3+b\\-2+3=b\\b=1\\\\y=-3x+1[/tex]
