given that sinx, tanx, and sin2x form geometric sequence, show cos^3x=1/2

Question

can someone explain this to me, i have no idea how to solve it. i really done understand how to turn it into a geometric sequence

Answer 1

just think back to your Algebra II. Terms of a GP have a common ratio, so

tanx/sinx = sin2x/tanx
1/cosx = = 2sinx*cosx * cosx/sinx
...