The Basis is Important!
If you are given coordinates and told to transform them using a matrix, you have not been given enough information to determine the final mapping.

Consider the matrix:
If we apply this matrix to coordinates there must be some implied basis, because coordinates alone are not geometric entities (a basis is required to convert coordinates into a vector). Assume this implied basis is. Thus, our coordinates describe the vector. The resulting transform,, will stretch this vector by a factor of 2 in the direction of the first element of the basis set. Of course that direction depends entirely on.

These illustrations show the significance of the basis when transforming vectors.
(Click on the images below)

Lecture 9   Slide 8   6.837 Fall '00