the important identity here is
cos(A+B) = cosAcosB - sinAsinB
So, it looks like you have
cos(6x+x) = cos 7x
You also know that
sin(A+B) = sinAcosB + cosAsinB
so,
sin(90+x) = sin90cosx + cos90sinx = 1*cosx = 0*sinx = cosx
Do lots of these, since they will come in handy later on.
Write the expression as a single trigonometric functions:
cos 6x cosx - sin6x sin x
if you could do it step by step?
also... How do I prove that sin(90deg + theta) = cos(theta)??
also step by step so i may learn?
1 answer
1 answer