+0

# Complex Numbers

0
127
1

Express (4 - 5i)(5 + 5i)(2 - 7i) in the form a + bi, where a and b are integers and i^2 = -1.

May 3, 2022

#1
+9461
+1

You can just expand it like i was a variable instead of a special number, and use the fact i^2 = -1 occasionally to reduce the power.

$$\quad(4 - 5i)(5 + 5i)(2 - 7i)\\ =(20 - 25i + 20i - 25i^2 )(2-7i)\\ = (20 - 5i -25i^2)(2 - 7i)\\ = (45 - 5i)(2 - 7i)\\$$

Can you continue from here, doing what I just did?

May 3, 2022