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*i*θ , obtain the trigometric identities for cos(θ1, θ2) and sin(θ1, θ2)

I think I have completed the real and imaginary solutions for the base e^+

*i*θ using the real part cos(θ1+θ2)and imaginary

*i*sin(θ1+θ2)

Gaining

cos(θ1 + θ2) = cosθ1 cosθ2 - sinθ1 sinθ2

sin(θ1 + θ2) = sinθ1 cosθ2 + cosθ1 sinθ2

My problem is how to proceed from here for the base e^-

*i*θ

should my real and imaginary parts be in the form

cos(θ1-θ2) +

*i*sin(θ1-θ2)

or

cos(θ1+θ2) -

*i*sin(θ1+θ2)

Thanks in advance for any help