Question

Which complex number has an absolute value of 5?
–3 + 4i
2 + 3i
7 – 2i
9 + 4i

Answer 1

2 + 3(-1) = -5 = 5 B.

Answer 2

if you have a complex number a+bi
then the "absolute value" | a+ bi | is the "distance" of the complex number from the origin.
say c is a complex number. Its length |c|^2 = c*conj(c)