# Homework Help: Can someone please help me understand this lesson? I tried, but I just can't get it !

1. Dec 22, 2011

### Dosirak

The lesson can be found at www.sol-ah.tumblr.com

And also some help with this question please ~

If Vector PQ = [-1 , 4]
Vector RQ = [2 , 1]
Vector RS = [-3 , 2]
what is Vector SP ?

Thanks!

2. Dec 22, 2011

### Mentallic

Is it possible to get a more zoomed in version of the lesson?

A diagram would be best to help you keep track of everything.

Start with a point P, and draw a vector to the point Q. To know which direction you need to roughly point towards, you can get an idea of this by looking at the components of the vector. PQ = [-1,4] which means that from P it heads -1 units in the x direction and 4 units in the y direction, so the vector is pointing in the NW direction and more North than West. Now keep a label of the x and y components of this vector by drawing a right triangle with the hypotenuse being the vector.

For the vector RQ notice that it is equal to -QR, which means you can instead draw QR = [-2,-1]. It's not necessary to do this, and if you can figure out where the point R should be located roughly in order for the vector to point to Q, then I'd say just skip it altogether.

Now do this for the rest of the vectors. Finally, draw the vector SP. Can you determine what its components are?

3. Dec 22, 2011

### cupid.callin

You can write $\vec{PQ} = \vec{OQ} - \vec{OP} = -\hat{i} + 4\hat{j}$
And you need $\vec{SP} = \vec{OP} - \vec{OS}$