2012 AMC 10B Problems/Problem 21
When you see a and 2a, you could think of 30-60-90 triangles. Since all of the other's lengths are a, you could think that b is root3a. The final diagram looks something like this: .---b---. a 2a a . a .
a a .
So, b=root3a, so B:A=root3a=(A)