1. Sine is the ratio opposite/hypotenuse
2. Cosine is the ratio adjacent/hypotenuse
3. Tangent is the ratio opposite/adjacent
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One way to remember is to use the acronym "SOH CAH TOA" which you can pronounce or read out as "soak a toe-ah"
SOH = sine, opposite hypotenuse
CAH = cosine, adjacent hypotenuse
TOA = tangent, opposite adjacent
There are probably many other ways to help remember the trig ratios, but I can't think of anything else off the top of my head.
