Question

Trigonometry , help pls......

Answer 1

prove..
\[\cos 2 \theta + \cos 4 \theta + \cos 6 \theta + 1 = 4 \cos \theta \cos 2 \theta \cos3 \theta \]

hence solve for theta ...
\[\tan ^{2} \theta + 2\cos 2\theta -1 = 0\]

Answer 2

hey .... I know how to the first one... but i can't use it to get the answer for the second one... I'm kinda stuck on the second one....

Answer 3

@Hero , @mathstudent55 , @wolfe8 , @thomaster

Answer 4

Lulz. I don't think I've ever seen this form yet.

Answer 5

@ganeshie8 can u help me?

Answer 6

@phi

Answer 7

I don't see how the first identity helps to solve the 2nd line...

Answer 8

me neither....

Answer 9

you can do the obvious, and use cos^2(x) - sin^2(x) = cos(2x)

Answer 10

or cos(2x)= 2cos^2(x) -1