#### Question

Given a triangle △ABC with AC=15 , BC=7 and

∠ACB=60 , find the value of AB .

Question

Given a triangle △ABC with AC=15 , BC=7 and

∠ACB=60 , find the value of AB .

Using the Law of Cosines

c^2=a^2+b^2-2ab\cos C

c^2 = 15^2+7^2-2\times 15\times 7\cos 60\degree

c^2 = 15^2+7^2- 15\times 7

=15\times 8+49

=169

\therefore c = 13