Question

simplify (11 + 4i)(-5 -9i)

Answer 1

Use FOIL to start.
Remember that \(i^2 = -1\).

Answer 2

okay thanks.

Answer 3

I got -55-99i-20-36i^2

Answer 4

So far, you are almost correct.
Just make sure the third term is -20i (add the i to what you have).
Now use the fact that \(i^2 = -1\) to simplify the term \(-36i^2\).

Answer 5

You should have this:

-55 - 99i - 20i - 36i^2

Now you can do two things.
1. Combine -99i and -20i since they are like terms.
2. Change i^2 to -1, and simplify the last term.

Answer 6

To check your answer, click on
https://www.wolframalpha.com/input/?i=%2811+%2B+4i%29%28-5+-9i%29

Answer 7

-55 - 119 ?

Answer 8

-55 - 119 i

Answer 9

okay thanks

Answer 10

YW

Answer 11

= -55 - 99i - 20i - 36i^2

The -99i term and the -20i term combine:

= -55 - 119i - 36i^2

i^2 = -1, so we substitute:

= -55 - 119i - 36(-1)

= -55 - 119i + 36

= -19 - 119i

That is the final answer.