Digital SAT · Math · Geometry and Trigonometry. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A right triangle has one 90° angle. The side opposite it, the hypotenuse, is the longest side. If you know two sides, the Pythagorean theorem gives the third.
Two special right triangles appear again and again: the 45°-45°-90° triangle (half a square) and the 30°-60°-90° triangle (half an equilateral triangle). Their side ratios are on the reference sheet, and they let you find sides without a calculator.
Sine, cosine and tangent are ratios of two sides, named from the angle you are using. They depend only on the angle, so similar right triangles have the same ratios.
Using a2 + b2 = c2 with the hypotenuse as one of the legs. When the longest side is known, subtract: leg2 = hypotenuse2 − other leg2.
Answer: sin Y = cos X = 3/5
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