I have been working on showing the equality between(adsbygoogle = window.adsbygoogle || []).push({});

N=0 to ∞ Ʃ cos(2nθ)(-1)^n/(2n)! = cos(cos(θ))cosh(sin(θ))

I started by using the standard series for cosine and putting cos(2nθ) in for the x term.

I did the same for cosh(sin(θ)). I manipulated the forms every way I could think but it never looked anything like the answer I seek.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Help with a trig to sum identity.

**Physics Forums | Science Articles, Homework Help, Discussion**