Question

Can anyone explain how to do this?

The gradient of line q: y = ax + b is -4. Line q passes
through point P(-3,21). Calculate the values of a and b.​

Answer 1

a = - 4, b = 9

Explanation:

The equation of a line in slope- intercept form is

y = mx + b ( m is the slope and b the y- intercept )

y = ax + b is in this form

with slope = a = - 4

y = - 4x + b ← is the partial equation of the line

To find b substitute (- 3, 21) into the partial equation

21 = 12 + b ⇒ b = 21 - 12 = 9