Vector Problem:
In triangle ABC, let vector u = AB and vector v = BC. Let M be the midpoint of AB and N be the midpoint of BC. Write each of the following in terms of u and v.
a. BA
b. CA
c. MN

Question

Vector Problem: 
In triangle ABC, let vector u = AB and vector v = BC. Let M be the midpoint of AB and N be the midpoint of BC. Write each of the following in terms of u and v.
a. BA
b. CA
c. MN

anonymous · Answer

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phi · Answer

use a -  to change the direction of a vector.    -AB = BA
you can see that AB + BC  gets you from A to C, that is, AB+BC is AC

you can get from M to N  by MB  and then BN
MB is 1/2 AB  and MN is 1/2 BC

anonymous · Answer

In terms of vectors u and v (u = AB, v = BC):

a. BA = -u
b. CA = -v - u
c. MN = (u/2) + (v/2)

Do these answers seem correct?

phi · Answer

yes, they look good. 

of course, you might see (obvious) variations
CA = -(u+v)
MN= (u+v)/2

anonymous · Answer

Right, that would make it simpler. Thanks for your help