I'm sure that I'm missing an identity here, but how do I get from: -4cos(t)cos(2t)-2sin(t)sin(2t) to -4cos^{3}(t) Thanks for any help.
Follow Math Help Forum on Facebook and Google+
Originally Posted by MajMinor I'm sure that I'm missing an identity here, but how do I get from: -4cos(t)cos(2t)-2sin(t)sin(2t) to -4cos^{3}(t) Thanks for any help. Use the product to sum identities to get $\displaystyle -4\left( \frac{\cos(3t)+\cos(t)}{2} \right)-2\left( \frac{\cos(t)-\cos(3t)}{2} \right) = -\cos(3t)-3\cos(t)$ by the triple angle forumla you get the desired result $\displaystyle -4\cos^3(t)$
Thanks for the help.
View Tag Cloud