# Problem with mathematical induction

• Sep 20th 2012, 05:06 AM
alireza1992
Problem with mathematical induction
Hi, I tried everything I could think of, but I cannot solve this problem. Any idea? (look at the image bellow)

Attachment 24865
• Sep 20th 2012, 05:38 AM
emakarov
Re: Problem with mathematical induction
In the inductive step, you need to show $\frac{1-\cos2n\theta}{2\sin\theta}+\sin(2n+1)\theta=\frac{ 1-\cos(2n+2)\theta}{2\sin\theta}$. Multiply both sides by $2\sin\theta$ and use the formula for the difference of cosines.