Question

What would be equivalent to (4 + 5i)(4 - 5i)?

Answer 1

foil it

Answer 2

or , you can use the formula
(a+b)(a-b)=a^2-b^2

Answer 3

so, (4 + 5i)(4 - 5i)
= 4^2-(5i)^2
=16- 25i^2

Answer 4

can you go from there?

Answer 5

multiply a complex number by its complex conjugate, you get real number
\[(a+bi)(a-bi)=a^2+b^2\]

Answer 6

oh wow, i"ve actually never learned the foil method this is new to me lol

Answer 7

don't think about \(i\) and don't think about minus signs
just \(4^2+5^2\)

Answer 8

hmm, that's to confusing

Answer 9

really? foiling is confusing, sum of squares is pythagoras

Answer 10

i would say use your knowleg about real algebra and keep in mind that i*i = -1

Answer 11

Ok, thanks you guys :)