Simplify conjugate expressions

1. Nov 29, 2004

aisha

1) (-7+20)(-10-3i)

2) (-2-5i)/(3+4i)

I dont think I did these two questions right does anyone know how?

2. Nov 29, 2004

arildno

Multiply with 1, written in terms of the conjugate expressions of the denominators.

3. Nov 29, 2004

aisha

I simplified (-7+2i)(-10-3i) and got 76+i is this correct?

4. Nov 29, 2004

cdhotfire

yes, that is correct.

5. Nov 29, 2004

HawKMX2004

1) (-7+20)(-10-3i)

Step 1.) FOIL the Problem
Step 2.) Simplify from there (Do addition Subtraction etc.)

2) (-2-5i)/(3+4i)

I forgot how to do division with imaginary numbers I'll try to look it back up and give you some help

6. Nov 29, 2004

kreil

All you need to know to solve these sort of problems is that:
$$i=\sqrt{-1}$$
$$i^2 = -1$$
$$i^3 = -i$$
$$i^4 = 1$$ and the cycle repeats

$$(-7+2i)(-10-3i)$$
$$70+21i-20i-6i^2$$
$$76+i$$

you did in fact do it correctly.

7. Nov 29, 2004

cdhotfire

hey, for that latex all i have 2 do is put [-code-] the code and end. Correct?
let me try.
seems i have 2 put latex
[Latex]\theta[/Latex]

Last edited: Nov 29, 2004
8. Nov 29, 2004

aisha

Thanks for taking the time to look it up, and thanks everyone who told me the first one is right what a relief! For simplifying (-2-5i) / by (3+4i) I got (-26-7i)/25 as my final answer can someone tell me is this right?

Last edited: Nov 29, 2004
9. Nov 30, 2004

yes you are right again
(-2-5i)/(3+4i) does equal (-26-7i)/25

10. Nov 30, 2004

aisha

Yay!!

Thanks sooo much! :tongue2: If anyone has any objections they may still speak