Math Help - How to prove this ?

1. How to prove this ?

Stucked on this for hours

Given, √2cosA=cosB+cos³B and √2sinA=sinB-sin³B

need to prove that,
sin(A-B)=±1/3

Somebody pls give the solution, thanks

3. Re: How to prove this ?

Yayyyyyyyy!!! That was just AWESOME!! Many many thanks!