Question

sin7alfa•cos 4alfa+sin 4alfa •cos 7alfa -3sin 11alfa=?
sin2xcos3x-2sin5x+cos2xsin3x=
cos2,5xcos1,5x+cosx+sin1,5xsin2,5x=?
2(cos4x•cos7x+sin2x)+2•sin4x•sin7x=?

Answer 1

1)Sin7αCos4α +Sin4αCos7α -3Sin11α = Sin11α - 3Sin11α = -2Sin11α
 2)Sin2xCos3x-2Sin5x+Cos2xsin3x=Sin5x -2Sin5x = -Sin5x
3)Cos2,5xCos1,5x+Cosx+Sin1,5xSin2,5x= Cosx +Cosx = 2Cosx
4)2(cos4x•cos7x+sin2x)+2•sin4x•sin7x=
=2Cos4xCos7x +4Sin2x +2Sin4xSin7x = 
=2(Cos4xCos7x +Sin4xSin7x) +4Sin2x = 2Cos3x + 4Sin4x