Integral of an exponential divided by a root function

[chaoseverlasting]

Homework Statement

Prove that the diagonals of a parallelogram bisect each other.

Homework Equations

I chose one vertex as the origin, one as a and one as b. The final vertex was a+b.

The Attempt at a Solution

The diagonals were \vec{r_1}=\vec{a}+\vec{b} and \vec{r_2}=\vec{b}-\vec{a}. Where do I go from here? Can I assume that they go through the center of the parallelogram or do I have to prove that too?

 

[EnumaElish]

What is the definition of a vertex?

 

[chaoseverlasting]

Err... a point where two vectors intersect?

 

[HallsofIvy]

Your vectors "begin" at one vertex, right? What vector, starting at that vertex, has its "end" at the midpoint of \vec{a}+ \vec{b}? \vec{b}-\vec{a}?
(Note that, since \vec{b}-\vec{a} "starts" at \vec{a} instead of the origin, the midpoint of \vec{b}-\vec{a} is at \vec{a} plus half of \vec{b}-\vec{a}.)