# Linear Algebra Special Matrices Problem!

• Sep 1st 2008, 02:13 PM
Skerven
Linear Algebra Special Matrices Problem!
What 2 by 2 matrix P projects the vector (x,y) onto the x axis to produce (x,0)?
What matrix Q projects onto the y axis to produce (0,y)?
If you multiply (5,7) by P and then multiply by Q, you get (_____) and (_____). (Fill in the vector-blanks)
*the vectors in part three arent neccessarily 5 dimensions!)

I'm pretty sure I found P and Q, but for the third problem I only got 1 vector...

Q= [
001
100
010]
P= [
010
001
100]
P*Q*(5,7)=(0,0)=0 ... And yet the problem asks for two (i'm assuming nonzero) vectors... What have i done wrong?

(PS Im on my blackberry!)
• Sep 2nd 2008, 03:21 AM
horseypie
well the matrix to extract the x-coordinate of a vector, i.e. [P] is
1 0
0 0

and [Q] would be
0 0
0 1

I don't know why you got 3x3 matrices when you're only working in a 2x2 space...hopefully it should work out for you now

also the first answer will be (5,7).P and the second answer will be (5,7).Q (i think anyway)