Find a vector v with a given magnitude in the direction

**icelated** · January 11th 2012, 02:08 PM

Find the vector v with magnitude 2.7 in the direction of w = < 1, -2, -1 >

This is what i have so far and i will point out where i am stuck.

$|| w || = \sqrt {1^2 + (-2)^2 + (-1)^2 } = \sqrt 6$

$v = 2.7 \frac{w} {|| w ||}$

so, filling in for w we have

$2.7 ( \frac{1} {\sqrt 6} , \frac{-2} {\sqrt 6} , \frac{-1} {\sqrt 6})$

Now, from here do i just multiply the 2.7 to the numerator?

A Similar problem in my book, the solution manual does something weird and i cant figure it out like

$5 \frac{u} {|| u ||} = 5 < \frac {-1}{\sqrt 5} , \frac{2}{\sqrt5} >$

Then, they go to this final step and i dont see how they are doing that?

$< - \sqrt 5 , 2 \sqrt 5 >$

**emakarov** · January 11th 2012, 02:15 PM

Originally Posted by icelated

Now, from here do i just multiply the 2.7 to the numerator?

Yes.

Originally Posted by icelated

A Similar problem in my book, the solution manual does something weird and i cant figure it out like

$5 \frac{u} {|| u ||} = 5 < \frac {-1}{\sqrt 5} , \frac{2}{\sqrt5} >$

Then, they go to this final step and i dont see how they are doing that?

$< - \sqrt 5 , 2 \sqrt 5 >$

Recall that $5/\sqrt{5}=\sqrt{5}$ .

**icelated** · January 11th 2012, 02:21 PM

thank you

**CaptainBlack** · January 12th 2012, 11:51 PM

Originally Posted by icelated

thank you

Use the thanks button, don't just make a post saying thanks

CB

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