# Vector real simple question

• Apr 14th 2010, 01:25 PM
darklight
Vector real simple question
Only two simple questions
(REally i am not good at math and i am in the 10th grade)
This is my first post and hope to get some little help .In the summer i have tryed hacking now math has replaced hacking :)
+ or -
First : http://i41.tinypic.com/11cgvug.jpg

Second : 2MN=6i how to solve this ?
(MN and i are in vector with an index "-->")

Note : if the post looks bad with the big picture i will replace that with a link
• Apr 15th 2010, 12:12 AM
Hello darklight

Welcome to Math Help Forum!
Quote:

Originally Posted by darklight
Only two simple questions
(REally i am not good at math and i am in the 10th grade)
This is my first post and hope to get some little help .In the summer i have tryed hacking now math has replaced hacking :)
+ or -
1-

$\frac{-\vec a +3\vec b-2 \vec c}{7}$, when $\vec c= \binom 12$
Of the two answers you give, the one with the $+$ sign is correct:
$\frac{-\vec a +3\vec b+ \binom{-2}{-4}}{7}$
since you have taken the $-$ sign into account by mutliplying $\binom12$ by $-2$ to get $\binom{-2}{-4}$.

Quote:

Originally Posted by darklight
2- 2MN=6i how to solve this ?
(MN and i are in vector with an index "-->")

$2 -2\vec{MN} =6\vec i$
If so, it doesn't make sense, since $2$ is a scalar and $\vec{MN}$ and $\vec i$ are vectors. You can't add vectors and scalars like this.

What did you really mean?

• Apr 15th 2010, 12:26 AM
darklight

In the second question is my fault, didn't write that M(-3:-2) and N(x;y)
I have to find the coordinates of N ?
2MN=i
• Apr 15th 2010, 02:21 AM
earboth
Quote:

Originally Posted by darklight

In the second question is my fault, didn't write that M(-3:-2) and N(x;y)
I have to find the coordinates of N ?
2MN=i

The wording of the question isn't clear to me so I'm just guessing:

1. If M(-3, -2) and N(x, y) then

$\overrightarrow{MN} = (x, y)-(-3,-2)=(x+3 , y+2)$

2. If

$2 \overrightarrow{MN} = 6i$ (I'll trake the original version of the equation. See your 1st post) that means:

$(2x+6 , 2y+4) = (6,0)~\implies~\begin{array}{l}2x+6=6\\2y+4=0\end{ array}$

3. Solve these equations for x and y respectively. You'll get N(0, -2)
• Apr 15th 2010, 08:51 AM
darklight
thanks a lot ,this was what i asked for........