Question

Perform the indicated operation & simplify. Express the answer in terms of i (as a complex number). ( 5 − 7 i ) ( − 9 + 4 i )

Answer 1

83i - 17

Explanation:

(5 - 7i)(-9 + 4i)

FOIL:

5(-9) - (7i)(-9) + (5)(4i) + (-7i)(4i)

-45 + 63i +20i -28i^2

-45 +83i +28

83i - 17

Answer 2

(5 - 7i)(-9 + 4i)

To solve this question you must FOIL (First, Outside, Inside, Last) like so

First:

(5 - 7i)(-9 + 4i)

5 *(-9)

-45

Outside:

(5 - 7i)(-9 + 4i)

5 * 4i

20i

Inside:

(5 - 7i)(-9 + 4i)

-7i * -9

63i

Last:

(5 - 7i)(-9 + 4i)

-7i * 4i

-28i²

^^^There are two i that you need to multiply. This will give you i²

Now combine all the products of the FOIL together like so...

-45 + 20i + 63i + (-28i²)

-28i² + 20i + 63i - 45

NOTE: i² = -1

-28(-1) + 20i + 63i - 45

28 + 20i + 63i - 45

Combine like terms:

83i - 17 <<<This is your answer

Hope this helped!

~Just a girl in love with Shawn Mendes