# Homework Help: 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
$$\theta$$

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