Question

What is an equation of the line that passes through the point (1,-3) and is perpendicular to the line x+3y=21?

Answer 1

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