Physics
posted by Cathy .
You are given vectors A = 5.0i  6.5j & B = 3.5i + 7.0j. A third vector C lies on the xyplane. Vector C is perpendicular to vector A, & the scalar product of C with B is 15.0. From this information, find the components of vector C.

A=[5,6.5]
B=[3.5,7]
If A is perpendicular to C, then A.C=0, or
C=[6.5k, 5k]
(verify that A.C=0)
If in addition, C.B=15, we have
C.B=[6.5k,5k].[3.5,7]
=35k22.75k
=12.25k
But C.B=15, therefore 12.25k=15, =>
k=15/12.25=60/49
Therefore
C=[6.5k,5k]
=[390/49, 300/49]
Check my arithmetic and that the given conditions are satisfied. 
thanks

you're welcome!

I don't understand the flow in the math here. Please help me understand this solution by "dumbing it down" a bit.