Question

What is the product of (2+7i)(2-7i) in the from a+bi

Answer 1

i = sqrt(-1), i^2 = -1

So multiplying it out;

4 - 14i + 14i - 49i^2

4 - 49 * -1

= 53

Answer 2

Explanation:

(2+7i)(2-7i) = 2² - (7i)² { ( a+b) (a-b) = a²-b² }

= 4 - 7² * i²

= 4 - 49* (-1)

= 4 + 49

= 53