show that cos 3(theta) = 4cos^3(theta)-3cos(theta) where do i even start?
Follow Math Help Forum on Facebook and Google+
Is this want you would like to prove?
yess... thanks for making it the way it should!
Originally Posted by ohhhh show that cos 3(theta) = 4cos^3(theta)-3cos(theta) where do i even start? Now apply the formula as well as the double-angle formula for sine and for cosine.
ok, so let me see. cos (2a+a) = cos2(a)*cos(a) - sin2(a)*sin(a) = cos^2a-sin^2a - 2sin(a)*cos(a)*sin(a) = cos^2a-sin^2a - 2sin^2(a)*cos(a) ...is this right so far?
Originally Posted by ohhhh show that cos 3(theta) = 4cos^3(theta)-3cos(theta) Complex numbers also work: So
thanks a lot for your help guys. got it down!
cos (2a+a) = cos2(a)*cos(a) - sin2(a)*sin(a) right = cos^2a-sin^2a - 2sin(a)*cos(a)*sin(a) You have lost a cos(a). It should read
View Tag Cloud