55.3k views
5 votes
In aΔABC, if ∠B = 60° and the ratio of two sides is a : c = 2 : √3 + 1, then ∠A= ____.

A: 45
B: 40
C: 35
D: 55

User Meligira
by
6.9k points

1 Answer

2 votes

To calculate for the value of ∠ A, let us first find for the length of side B using the cosine law:

b^2 = a^2 + c^2 – 2 a c cos B

b^2 = 2^2 + (√3 + 1)^2 – 2 (2) (√3 + 1) cos 60

b^2 = 6

b = 2.45

Given two sides and the angle in between, we can calculate for ∠A using the sine law:

b / sin B = a / sin A

2.45 / sin 60 = 2 / sin A

sin A = 0.707

A = 45˚

Therefore the answer is letter A: 45

User MGH
by
7.9k points