I need to be pointed in the right direction. In a program that I'm writing I need to draw an arrow. I have a line that can be any random angle. What formula can I use to draw two other lines that begin at an X2,Y2 point and are slanted at a 45 degree angle for instance. The endpoints of the lines that make up the arrow does not matter.

For example:

X1=0
Y1=0
X2=10
Y2=10

How can I plot an arrow off of theese points using a formula?

Thanks for any help.