# Finding a vector

• Jun 5th 2010, 11:33 AM
Mukilab
Finding a vector
P is the point 2,3
Q is the point 6,6

Write down vector PQ in column form. I got 4 over 3 (not sure how to use latex with this one)

The question:

PQRS is a prallelogram
Vector PR (not sure how to make the vector sign in latex) = 4 over 7
Find vector QS

I did -4 over -4 + 0 over 4 and got -4 over 1 as an answer.

Correct?
• Jun 6th 2010, 12:42 AM
Mukilab
Anyone?
• Jun 6th 2010, 01:14 AM
running-gag
Hi

Your answer is correct but I haven't understood how you got it

$\vec{PR} = \binom{4}{7}$

$\vec{PQ} = \binom{4}{3}$

$\vec{QS} = \vec{QP} + \vec{PR} + \vec{RS} = 2 \vec{QP} + \vec{RS} = \binom{2 \times (-4) + 4}{2 \times (-3) + 7} = \binom{-4}{1}$
• Jun 6th 2010, 01:25 AM
Mukilab
$\vec{QR}=\vec{PS}$
$\vec{PQ}=\vec{SR}=\binom{4}{3}$

Because $\vec{PR}=\binom{4}{7}$
$\vec{QR}=\binom{0}{4}=\vec{PS}$

Because $\vec{QS}=\vec{-PQ}+\vec{PS}$
$\vec{QS}=\binom{-4}{-3}+\binom{0}{4}=\binom{-4}{1}$
• Jun 6th 2010, 01:32 AM
running-gag
Well done (Clapping)
• Jun 6th 2010, 02:18 AM
Mukilab
thanks