How it works
With one acute angle and any one side, a right triangle is fully determined. Side a is opposite angle A, side b is adjacent to it, and c is the hypotenuse.
The trig ratios link them. Remember SOH-CAH-TOA: sine = opposite/hypotenuse, cosine = adjacent/hypotenuse, tangent = opposite/adjacent. The other acute angle is 90° minus A.
Formula
sin A = a/c; cos A = b/c; tan A = a/b; B = 90° − A
Questions people ask
How do I find the height of a tree with trig?
Stand a known distance from the base (the adjacent side) and measure the angle up to the top. Height = distance × tan(angle), plus your eye height.
What if I know two sides instead of an angle?
Use the Pythagorean theorem for the third side and inverse trig for the angle: A = arctan(a/b), or A = arcsin(a/c).
Should my calculator be in degrees or radians?
This calculator takes degrees. Radians = degrees × π/180, so 30° is about 0.5236 rad.