Answer:
x + 3y =21 equation 1
let the equation perpendicular to X + 3y = 21 be
3x - y + k = 0 equation 2
since the point ( 1 , -3 ) passes through equation 3x - y +k =0
3× 1 - (-3) + k = 0
or, 3 + 3 + k = 0
or, 6 + k =0
or, k = -6
now,
putting the value of k in equation 2
3x - y + k = 0
or, 3x -y -6=0
