There are two ways to work this out: normal variables or using "imaginary" numbers.
Normal variables:
[tex] (7+2i)(3-i)\\(7*3)+[7*(-i)]+(3*2i)+[2i*(-i)]\\21-7i+6i-2i^{2}\\\\21-i-2i^{2}[/tex]
Imaginary numbers:
Using the result from earlier:
[tex]21-i-2i^{2}[/tex]
Now since [tex] i = \sqrt{-1}[/tex], then the expression becomes:
[tex] 21-i-2i^{2}\\21-i-2(\sqrt{-1})^{2}\\21-i+(-2)(-1)\\21-i+2\\\\23-i[/tex]
