Original post by jeja12
tan(3x)=3tanx-tan^3(x)/1-3tan^2x
Split into tan(2x + x).
That gives you (tan 2x + tan x) / (1 - tan 2x tan x)
now use tan 2x = 2 tan x / (1- tan^2 x).
Original post by jeja12
thx
No problem.
Original post by Zacken
cos 4a = cos (2(2a)) = 2cos^2 2a - 1= 2(1-cos^2 a)^2 - 1
how did you factorise 2cos^2 2a -1 into that
Original post by jeja12
how did you factorise 2cos^2 2a -1 into that
What I wrote was wrong, I'll delete it, sorry.
What I meant was: cos 4a = cos (2(2a)) = 2cos^2 2a - 1
The cos 2a = 2cos^2 a - 1
So plug that in:
2 (cos 2a)^2 -1 becomes 2(2cos^2 a -1)^2 - 1
Original post by jeja12
I get it now thank you very much 
No problem!
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