Think of a 5-12-13 triangle (that’s one of the Pythagorean triples you should know).
Say angle A measures x°, which would make angle C measure (90 – x)°. (I’m choosing those based on the fact that I already know that the sine of angle C will be 12/13.)
Now that we’ve got it set up, all we need to do is SOH-CAH-TOA it: sin x° = 5/13.
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