加法定理が使える形になるよう、変形します。
(1)
sin(π/4) = cos(π/4) = 1/√2 を利用
-sinθ + cosθ = -√2(sinθ*1/√2 - cosθ*1/√2)
= -√2{sinθ*cos(π/4) - cosθ*sin(π/4)}
= -√2*sin(θ-π/4)
(2)
cos(π/3) = √3/2 , sin(π/3) = 1/2 を利用
√6*cosθ + √2*sinθ = 2√2(cosθ*√3/2 + sinθ*1/2)
= 2√2{cosθ*cos(π/3) + sinθ*sin(π/3)}
= 2√2*cos(θ-π/3)