.
Let me make writing more understandable for this problem.
Let i = (1,0,0) be the first given vector,
j = (0,1,0) be the second given vector,
and k = (0,0,1) be the third given vector.
We also have m = (0,1,1) as the fourth given vector.
Let c = a*i + b*j + c*k be an arbitrary vector of your 3D space.
Then it has TWO different presentations.
One is this c = a*i + b*j + c*k. (1)
The second is this: c = a*i + b*m + (c-b)*k. (2)
(Check it by considering its by-component parts.)
These two presentations of the same vector give you the example you are looking for.