The expression
cos x + cos 3x + cos 7x + cos 9x
can be written in the equivalent form a cos bx cos cx cos dx for some positive integers a, b, c, and d.
Find a + b + c + d.
See here :
https://web2.0calc.com/questions/halp_109#r3
Thanks Heureka and CPhill!
HAHAHA!!!!.....most of the thanks should go to Heureka!!!!
