Mechanics Help

[datfatcat]

If the question (say a slope question for example) does not say we need to use i and j, do we need to use them?  Or can we just write Perpendicular to slope and Parallel to slope?  Cause I wrote perpendicular and parallel and lost marks in a practice exam because teacher said I have to use i and j, even though question hasn't said so.

Edited: Some text books say you need to, but Derrick Ha's one doesn't.  Also, my teacher said i and j can only be used on dynamic, not statics.  Is that right?

[sahil26]

Well i think you can use basic physics to find the answer. So i totally get how to can do it.
Perhaps, the answer had to be in i and j form?
Usually if the answer is a discrete numerical value... you should OK.
Exact values require i and j form.