[tex]\left \{ {{-1=3a+b} \atop {5=-a+b /*(-1)}} \right. \\+\left \{ {{-1=3a+b} \atop {-5=a-b}} \right. \\-1-5=3a+a\\-6=4a /:4\\-\frac64=a\\a=-\frac32\\\\5=\frac32+b /-\frac32\\3\frac42-\frac32=b\\b=3\frac12\\\\y=-\frac32x+\frac72\\y=-(\frac32x-\frac72)\\y=-\frac{3x-7}2[/tex]
