For solve by using quotient rule, the result will be a complex form. So, for the simplicity we can take an easy method - substitution method. This is the complex number form, so better to substitute the value to an exponent form cos θ + i sin θ = eiθ sin θ + i cos θ = i[
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sinθ+cosθ] = i [- i sin θ + cos θ] = i [cos θ - i sin θ] = ie−iθ (