- sinθ + 2sin(π/2-θ)=0

- sinθ + 2cosθ =0

sinθ = 2cosθ

tanθ =2

(2)sinθcosθ + sin？ θ-2cos？ θ uses the reduced power formula.

=( 1/2)sin 2θ+( 1-cos 2θ)/2-( 1+cos 2θ)

= (1/2) sin2θ-(3/2) cos2θ-1/2 Use the general formula.

= 4/5

2. 0 < θ < 180 is known.

And 180 < 2θ< 270→90.