Question

"Write the equation of the line that is perpendicular to the line x - 4y = 20 and passes through the point (2, -5)." Thank you in advance!

Answer 1

y= -4x +3

Explanation:

① Rewrite the equation in the form of y=mx+c, to find the gradient of the given line, m.

x -4y= 20

4y= x -20

y= ¼x -5 (÷4 on both sides)

∴ Gradient of line= ¼

② Find the gradient of the new line.

The product of the gradients of perpendicular lines is -1.

¼(gradient of line)= -1

gradient of line

= -1 ÷¼

= -1 ×4

= -4

③ Substitute the value of the gradient into the equation.

y= -4x +c

④ Find the value of c by substituting a pair of coordinates.

When x= 2, y= -5,

-5= -4(2) +c

-5= -8 +c

c= -5 +8 (+8 on both sides)

c= 3

Thus, the equation of the line is y= -4x +3.