Question

In triangle ABC, AB = BC. If angle A = (4x - 30)° and angle C = (2x + 10)°, find the number of degrees in angle B.

a. 20
b. 40
c. 50
d. 100
e. 80

Answer 1

e. 80

Explanation:

A

/\

/ \

/ 4x-30 \

/ \

/ \

B / 2x+10 \ C

-----------------------------------------------

Since AB = BC, m<A = m<C.

4x - 30 = 2x + 10

2x = 40

x = 20

m<A = 4x - 30 = 4(80) - 30 = 50

m<C = m<B = 50

m<A + m<B + m<C = 180

50 + m<B + 50 = 180

m<B = 80