# help with vectors

Discussion in 'Math' started by Omega, Apr 20, 2009.

1. ### Omega Thread Starter Member

Feb 23, 2009
15
0
Hello every one I have this vector relation
E=A+$\alpha$(HXA) where E,A and H are vectors I want to proof that A=(E-$\alpha$(HXA))/$\sqrt{1+H^{2}\alpha^{2}}$
any one remeber how we can do this using vector identities or simple geometry or both of them (may be)?

2. ### Ratch New Member

Mar 20, 2007
1,068
4
Omega,

Just so there is not doubt, define what the capital H and alpha, both under the square root sign mean.

Ratch

3. ### Mark44 Well-Known Member

Nov 26, 2007
626
1
Starting with E=A+$\alpha$(HXA),
subtract $\alpha$(HXA) from both sides, which gives you
A=(E-$\alpha$(HXA))

I have no idea how you got the radical in there that you show.

4. ### Omega Thread Starter Member

Feb 23, 2009
15
0
sorry the correct equation is A=(E-$image=http://forum.allaboutcircuits.com/mimetex.cgi?\alpha&hash=74979a69d93b5d9a9b1d0e32b2acce2e$(HXE))/(1+$\alpha$$^{2}$H$^{2}$) I am realy sorry for this mistake. both of E and H are vectors with magnitudes E and H respectively and $\alpha$ is just a constant
I tried the method of Mark44 but it did not give me the factor 1/(1+$\alpha$$^{2}$H$^{2}$)

5. ### Ratch New Member

Mar 20, 2007
1,068
4
Omega,

Is this correcting the first or the second equation of your problem? You really should completely restate the problem after checking it carefully for typos and other errors so we don't have to guess what it means.

Ratch

6. ### Omega Thread Starter Member

Feb 23, 2009
15
0
ok from the begining: it is given that E=A+$image=http://forum.allaboutcircuits.com/mimetex.cgi?\alpha&hash=74979a69d93b5d9a9b1d0e32b2acce2e$(HXA) I need to proof the expression:
A=(E-$image=http://forum.allaboutcircuits.com/mimetex.cgi?\alpha&hash=74979a69d93b5d9a9b1d0e32b2acce2e$(HXE))/(1+$image=http://forum.allaboutcircuits.com/mimetex.cgi?\alpha&hash=74979a69d93b5d9a9b1d0e32b2acce2e$$image=http://forum.allaboutcircuits.com/mimetex.cgi?^{2}&hash=a71caff8b63d46a5dc1ed5390d39772c$H$image=http://forum.allaboutcircuits.com/mimetex.cgi?^{2}&hash=a71caff8b63d46a5dc1ed5390d39772c$) where A, E, and H are vectors and H is the magnitude of H and $image=http://forum.allaboutcircuits.com/mimetex.cgi?\alpha&hash=74979a69d93b5d9a9b1d0e32b2acce2e$ is just a constant

Mar 20, 2007
1,068
4
8. ### Omega Thread Starter Member

Feb 23, 2009
15
0
yes I did thanks.

9. ### killerfish Member

Feb 27, 2009
18
4
Hi guys,

currently im teaching myself vector, any of u guys could recommend good online sites that teach vectors from stretch to advance? I did a google around, i couldnt find any site cover in-depth/details about it rather just brief one. And I couldnt get any course notes to help me. Hope u guys lent me a hand.

Thanks.

Last edited: Jun 1, 2009

Feb 23, 2009
15
0