This is a nice place to point out that Trigonometry as practiced relies mostly on the two simplest right triangles, half an equilateral triangle giving a 30/60/90 right triangle, and half a square giving 45/45/90. Learn these cold and you've mastered half of Trigonometry. It should take about fifteen minutes.
Half a square means the two legs of the isosceles right triangle are the same length, last choice:
The length of the side opposite the 45° angle equals the length of the side adjacent to the 45° angle.
