Question

A is the point with coordinates (4, 6)

B is the point with coordinates (d, 21)

The gradient of the line AB is three.

Work out the value of d.

Answer 1

The gradient is the slope.

Slope is the change in y over the change in x.

3 = (21-6) / (d-4)

Simplify:

3 = 15/(d-4)

(D-4) = 15/3

D-4 = 5

Add 4 to both sides :

D = 9