Question

Which is equivalent to (4 + 5i)(4 - 5i)?

Answer 1

mine said it was 41

Answer 2

Okay its topic is '' Multiplications in Algebraic expressions''
It is done with distributive property of multiplication to addition and subtraction.

(4+5i). (4-5i)

It's like (x+y)(x-y) rule.
The answer must be $x^{2} - y^{2}$
But I don't recommend you to memorise, you should solve it yourself! :)

Anyways, let's try solving it.
By the way, you must learn distributive property before solving once.

$(4+5i)(4-5i)$
$= *distributive Property* 16-20i+20i- 25i^{2}$
$= 16- 25i^{2}$

Hope it helps! 
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