Hello
an equation for the line in point-slope form and general form is :
y = ax+b a : slope ; the Passing through (x' ; y')
y' = ax'+b
y-y' =a(x-x') and : x' =2 y' = - 1
calculate a :
let : y = ax+b .....(D)
....3y-x=7....(D') or y = (1/3)x+7/3
.(D) perpendicular to(D') : slope (D) × slope (D') = -1
slope (D') = 1/3
slop(D)×(1/3) = -1
slope (D) = -3
equation for the line : y-y' =a(x-x')
y+1 =(-3) (x-2)