Proving triangles with vector methods

[crayzwalz]

Homework Statement

In the following diagram D and E are the midpoints of AB and AC. Use vector methods to prove that DE = 1/2BC

Homework Equations

DE = 1/2 BC

The Attempt at a Solution

AD = 1/2AB
AE = 1/2AC

AD + DE = AE
DE = -AE + AD
DE = -1/2AC + 1/2AD
IF BC = -AC + AB
AND DE = -1/2AC + 1/2AB
THEN 1/2BC = DE
Diagram -

 

[tiny-tim]

hi crayzwalz!

yes, that's correct, except …

i] your + and - are the wrong way round in

DE = -AE + AD
and
IF BC = -AC + AB

ii] you should write it all out in one sequence, with the first line

DE =

and the last line

= 1/2BC