If you want a simple no-math alternative, simply cut the first end of the board at 15-deg, then hold that end flat to the floor (or any other flat reference -- such as the tablesaw fence). Then take another board (or ruler, etc) 17" in length and scribe your cut mark relative to the floor, then cut this 15-deg angle as well. (Note: don't use your scribed line as a literal cut-line, but rather as a marker as to where to make your 15-deg miter cut.)
With this method you can get to within a small fraction of an inch of perfect without doing any math, and so long as you duplicate this piece for all the other legs, any minor error will be perfectly replicated and as such will not affect your final project (i.e. in most cases it matters very little whether it is 17-1/32" or 16-31/32" high, so long as all four legs are identical in length and angle the table will sit flat and square just the same).
You will have your leg with a 15-deg angle and you will have your table height of 17" without having to do any math whatsoever. Then simply duplicate that piece for the other 3 legs.
There's nothing wrong with brushing up on one's trigonometry, but we often over complicate things when we get hung up on the math rather than just laying it out and marking the wood.
