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View Full Version : 1+cos(2theta)+cos(4theta)+cos(6theta)=4cos(theta)c os(2theta)cos(3theta)


aldo63
Jul 9, 2015, 01:47 PM
Help identify identity

sidit
Jul 12, 2015, 04:20 AM
1+cos2@+cos4@+cos6@
=cos4@+cos2@ +1+cos6@
=2cos4+2/2 @.cos4-2/2 @+1+2cos**3@-1
[email protected]@ + 2cos**3@
=2cos3@(cos@ +cos3@)
2cos3@(2cos3+1/2 @.cos3-1/2 @)
[email protected]@.cos@
[email protected]@.cos@
[email protected]@.cos3@

kreysiz
Jul 19, 2015, 10:33 AM
use the identities:-
1) cos(2pi) = 1
2) cos2x + cos2y = 2*cos(x+y)*cos(x-y)