There are two sides which relate as 3:8 and they form the angle 60 degrees. Find the nearest sides of the angle. The third side is 21 cm.

I tried to use cosine theoreme and I assumed that the first side is a=3*x/11 and the second side is b=8*x/11 cm.

Cosine theoreme says that c^2=a^2+b^2-2ab*cos(gamma).

It's all right now.