Question

sinx-2ycosx=1-2y --->sin(x-f)=(1-2y)/√(1+y^2)

Answer 1

这是叠加公式

sinx-2ycosx=1-2y

√(1+4y²)[sinx/√(1+4y²)-2ycosx/√(1+4y²)]=1-2y

令1/√(1+4y²)=cosf 2y/√(1+4y²)=sinf

则√(1+4y²)(sinxcosf-cosxsinf)=1-2y

√(1+4y²)sin(x-f)=1-2y

sin(x-f)=(1-2y)/√(1+4y²)