Question

Find the product of the complex number and its conjugate. 1 + 2i

Answer 1

Let's take a+ib as the complex number. Then conjugate is a-ib. Can you multiply them and see?

Answer 2

(a+ib)(a-ib)

a^2-aib
aib -2ib
a^2-2ib

Answer 3

ib*ib=i^2b^2

Answer 4

Now i^2=-1 so u get -b^2

Answer 5

So now u have a^2-(-b^2)=a^2+b^2