# Vectors again

• May 25th 2011, 04:45 PM
IDontunderstand
Vectors again
v=-3i+j, w=4i-2j

Find:

1) 4v-3w does this equal -24i-2j

2) ||V+W|| does this equal [tex] \sqrt{i^2-j^2} [ /math] I have an error if I take out the space between [ / that I do not know how to fix.

3) How can I find the angle between v and w?
• May 25th 2011, 05:17 PM
skeeter
Quote:

Originally Posted by IDontunderstand
v=-3i+j, w=4i-2j

Find:

1) 4v-3w does this equal -24i-2j

yes

2) ||V+W|| does this equal [tex] \sqrt{i^2-j^2} [ /math] I have an error if I take out the space between [ / that I do not know how to fix.

$|v+w| = |i - j| = \sqrt{1^2 + (-1)^2} = \sqrt{2}$

3) How can I find the angle between v and w?

$v \cdot w = |v| |w| \cos{\theta}$

btw, [tex] tags don't work ... use [tex] tags
• May 25th 2011, 05:24 PM
IDontunderstand
I figured it out thanks