# Another vector

1. Sep 16, 2007

### B-80

Given d1 + 8d2 = 5d3, d1 - d2 = 9d3, and d3 = 2 i + 4 j, what are the following vectors?

(a) d1 =
(b) d2 =

I keep trying to do substituting equations, but I am getting them wrong, and help?

2. Sep 16, 2007

### Dick

You'll need to show an example of how you are getting them wrong before anyone can help. It's actually a pretty easy problem.

3. Sep 16, 2007

### B-80

easy, fooled me then
D3=2i+4j
d1=5d3-8d2
d2=-9d3+d1

so i am trying to combine these to give me the value of either only d1 or only d2, and no matter how I mess with them, I can't seem to be able to do it.

d1=10i+20j-18j-36j-d1 so I cant do this, plus its wrong

idk did I mess up the subbing eq's?

4. Sep 16, 2007

### Dick

Try subtracting the first two equations from each other. Doesn't that get rid of d1?

5. Sep 16, 2007

### B-80

could you be a a little more specific and in dx-dy and do you mean set equal or subtract?

6. Sep 16, 2007

### Mindscrape

You could do either a substitution or a subtraction. You will either see that d1 = blah, or eqn1 - eqn2 = something*d2 = blap - bleh.

Last edited: Sep 16, 2007
7. Sep 16, 2007

### Dick

I mean (d1+8d2)-(d1-d2)=5d3-9d3. What's that?