f(x)=根号2cos x + 2sin(x+π/4) 的振幅和周期

f(x)=√2cos x + 2sin(x+π/4)
=√2cosx+2(sinx*√2/2+cosx*√2/2)
=2√2cosx+√2sinx
=√10(2/√5*cosx+1/√5*sinx)
=√10(sinxcosθ+cosxsinθ) （令sinθ=1/√5,cosθ=2/√5)
=√!0sin(x+θ)
振幅为√10,周期为2π