(3+4i)(3-4i)

Answer 1

just expand it as if the i was a variable

(3+4i)(3-4i)
= 9 - 12i + 12i -12i^2, now remember i^2 = -1
= 9 - 12(-1)
= 9+12
= 21

Answer 2

wait when you factor it wouldnt it be 9-12i+12i-16i^2

Answer 3

of course, my silly error

Answer 4

its totally cool you have helped alot :)