A·cos(x) + B·sin(x + α)
= A·cos(x) + B·(sin(x)·cos(α) + sin(α)·cos(x))
= A·cos(x) + B·sin(x)·B·cos(α) + B·sin(α)·B·cos(x)
= A·cos(x) + B^2·cos(α)·sin(x) + B^2·sin(α)·cos(x)
= (A + B^2·sin(α))·cos(x) + (B^2·cos(α))·sin(x)
= C·cos(x) + D·sin(x)
mit C = A + B^2·sin(α) und D = B^2·cos(α)