2.1.3 So­lu­tion math­c­plx-c

Ques­tion:

Mul­ti­ply out $(2+3{\rm i})(2-3{\rm i})$ and then find its real and imag­i­nary part.

An­swer:

You get $2^2-(3{\rm i})^2$, which is $4+9$ $\vphantom0\raisebox{1.5pt}{$=$}$ 13 so the real part is 13 and the imag­i­nary part is zero.