1. ## Vectors

In the quadrilateral, ABCD, AB = r, BC = s, CD = t and DA = u

which of the following statements is true?

A.) r+s = t+ u
B.) r + s = t - u
C.) r - s = t - u
D.) r + s = -t - u
E.) r - s = u - t

my answer was A, but the book says its D

another question when subtracting vectors, do you just change the arrowhead of the negative vector of do you move the entire arrow to face the other direction?

2.) If m = 3i - 2j and n = i + j

a.) show that 2m + 4n is parallel to the x-axis

i know how to do the substitution bit, but how do i show that it is parallel

thanks alot guys

2. Hello,

Originally Posted by andrew2322
In the quadrilateral, ABCD, AB = r, BC = s, CD = t and DA = u

which of the following statements is true?

A.) r+s = t+ u
B.) r + s = t - u
C.) r - s = t - u
D.) r + s = -t - u
E.) r - s = u - t

my answer was A, but the book says its D
$\displaystyle \vec{r}+\vec{s}=\vec{AC}$

But $\displaystyle \vec{t}+\vec{u}=\vec{CA}$ !

Draw a picture

another question when subtracting vectors, do you just change the arrowhead of the negative vector of do you move the entire arrow to face the other direction?
I don't understand ?

I think... :
If you want to draw a vector substracted to another, draw a line parallel to the vector, starting at the endpoint of the vector to which you are going to substract, but going the opposit direction.

2.) If m = 3i - 2j and n = i + j

a.) show that 2m + 4n is parallel to the x-axis

i know how to do the substitution bit, but how do i show that it is parallel

thanks alot guys
The x axis is defined by $\displaystyle \vec{i}$.
That is to say that a vector $\displaystyle \vec{v}$ is parallel to the x axis if and only if there exists k, such that $\displaystyle \vec{v}=k \vec{i}$