I need to work out both cos and sine of (2-i). The answer needs to be in the form x+iy where both x and y are real. So far I have got: cos (x) = ( e^ix + e^-ix ) / 2 as a general formula which when I substitute in gives: 0.5e^(2i+1) + 0.5e^(-2i-1) How do I get this into the correct form? and have I used the correct formula? Thanks, any help is welcome.