(5+2i) * (5+2i)
Distribute...
25 + 10 i + 10 i + 4i^2
Remember ... when there is a number with i^2 it will equal to (-1)...
So that means in this question .. I replace 4i^2 with - 4 because 4 ( -1) = -4
Now I can combine like terms....
25 + 10i + 10i - 4
Soo... The answer is 21 + 20i