Question

1.sinx+sin2x=1,then cos2x+xos4x=?

Answer 1

sinx+sin2x=1
so
sin2x=1-sinx
now
cos2x+cos4x
=1-2sin^2x+1-2sin^22x
=1-2sin^2x+1-2[1-2sinx+sin^2x]
=1-2sin^2x+1-2+4sinx-2sin^2x
=4sinx-4sin^2x

Answer 2

sinx+sin2x=1
=>sinx=1-2sinx
cos2x+cos4x
=1-2sin^2x+1-2(sin2x)^2
=4sinx-4sin^2x