Radar stations A and B are on an east-west line, 8.6 km apart. Station A detects a plane at C, on a bearing of 53 degree. Station B simultaneously detects the same plane, on a bearing of 323 degree. Find the distance from B to C.

That is the question. And Why can I not use cosine to find the lenth?

And I thank you in advance everyone who help me with this problem.