Attachment 25672

Find the values of x and y and write vector B.

xi+yj * 4i + 2j = -16

How do I find x and y?

Printable View

- November 12th 2012, 11:15 AMINeedOfHelpHelp finding a vector given two vectors?
Attachment 25672

Find the values of x and y and write vector B.

**xi+yj * 4i + 2j = -16**

How do I find x and y? - November 12th 2012, 11:22 AMMarkFLRe: Help finding a vector given two vectors?
Equate the dot product of A and B to -16, and to what should you equate the dot product of B and C?

Once you write these products, then you will two equations in*x*and*y*. - November 12th 2012, 11:30 AMINeedOfHelpRe: Help finding a vector given two vectors?
So...

(yj)(2j)+(xi)(4i)= -16

2yj^{2}+4xi^{2}= -16

So far is that right, or no? - November 12th 2012, 11:37 AMMarkFLRe: Help finding a vector given two vectors?
I would write:

Now, since and are perpendicular, to what will we equate their dot product? - November 12th 2012, 11:47 AMINeedOfHelpRe: Help finding a vector given two vectors?
B C

<2,1> * <2,3> = (4)+(3) = 7

That's not right, is it?

hdfhkfdg - November 12th 2012, 12:03 PMMarkFLRe: Help finding a vector given two vectors?
No, that's not right...you are taking the dot product of one half of A and C...you want to use B and C, and set it equal to what?

- November 12th 2012, 12:09 PMINeedOfHelpRe: Help finding a vector given two vectors?
Equal to 0 because they are orthogonal vectors??

- November 12th 2012, 12:11 PMMarkFLRe: Help finding a vector given two vectors?
Yes, exactly...good. So what equation results from this?

- November 12th 2012, 12:14 PMINeedOfHelpRe: Help finding a vector given two vectors?
2x+3y=0 ?

- November 12th 2012, 12:17 PMMarkFLRe: Help finding a vector given two vectors?
Great! (Cool) Now, you have:

(1)

(2)

Solve this system to get and . - November 12th 2012, 12:26 PMINeedOfHelpRe: Help finding a vector given two vectors?
So would vector B = <-6,4> ?

- November 12th 2012, 12:29 PMMarkFLRe: Help finding a vector given two vectors?
Yes, great work!

- November 12th 2012, 12:29 PMINeedOfHelpRe: Help finding a vector given two vectors?
Thank you so much! (: