Posted by skye on Thursday, August 16, 2012 at 11:24pm.
cos 2x = 2cos^2 x - 1
so, 1/2 cos x (1+2cos^2 x - 1) = cos^3 x
cos 4x = 1 - 2sin^2 2x
= 1 - 8sin^2 x cos^2 x
= 1 - 8sin^2 x (1 - sin^2 x)
= 1 - 8sin^2 x + 8 sin^4 x
cos 2x = 1 - 2sin^2 x
4cos 2x = 4 - 8sin^2 x
1/8(3-4cos2x+cos4x)
= 1/8(3 - 4 + 8sin^2 x + 1 - 8sin^2 x + 8 sin^4 x)
= 1/8(8sin^4 x)
= sin^4 x
Related Questions
Math - Trig - Double Angles - Prove: cos4x = 8cos^4x - 8cos^2x + 1 My Attempt: ...
Mathematics - Trigonometric Identities - Prove: sin^2x - sin^4x = cos^2x - cos^...
trig - how can you confirm the identity cos^4x = (1/8)(3+ 4cos2x+ cos4x) and ...
trigonometry - Verify that following are identities: 1. cos 3t = 4 cos³ t-3...
Trigonometry - Use the power-reducing formulas to rewrite the expression in ...
calc - Where do I start to prove this identity: sinx/cosx= 1-cos2x/sin2x please ...
Trig - prove the identity (sinX)^6 +(cosX)^6= 1 - 3(sinX)^2 (cosX)^2 sinX^6= ...
trigonometry HELP pleasE! - these must be written as a single trig expression, ...
Math - Calculus - The identity below is significant because it relates 3 ...
Math(Please help) - 1) Verify the identity cos^4x - sin^4x = cos2x I know that ...
For Further Reading
