Question

Use the exterior angle theorem to find the value of x in the triangle below.

A
x = 7

B
x = 5

C
x = 12

D
x = 15

Answer 1

Option A

Explanation:

By using the definition of an exterior angle of a triangle,

"Measure of the exterior angle of a triangle is equal to the sum of measures of the opposite interior angles"

m∠STP = m∠SWT + m∠STW

Substitute the measures of the angles from the picture attached,

15x = (7x + 1) + (7x + 6)

15x = (7x + 7x) + (1 + 6)

15x = 14x + 7

15x - 14x = 7

x = 7

Therefore, Option A will be the correct option.