i have no idea how to do these four problems please help me!!!
1. cos 2 x = cotx - tanx
sinx cosx
2. (cosx-sinx)^2 = 1 - sin 2 x
3. secx - sinxtanx = cosx
4. cos(x+y)cosy + sin(x+y) sin y = cosx
For Left Hand SideOriginally Posted by milkywayio
Express as,
Double angle for,
Thus,
For Right Hand Side,
Use reciprocal identities to get,
Add fractions,
Use double angle for cosine,
Express as,
Use double angle for sine,
Use identities,
Thus, the left hand and the right hand give the same result
Q.E.D.