Linear transformations and subspaces
Changing basis changes T. I assume that when b1=(1,1) this is b1 relative to the standard basis e1 and e2 (well, 'standard' doesn't matter  it's just another basis).
There are several ways to do this. You could just try to work out what Te1 and Te2 are from the action of T on b1 and b2 (e.g. note that e2=b2b1, so you know what Te2 is now, but don't forget to express Te2 in terms of e1 and e2.).
