Trigonometry is a branch of math that deals with triangles. Lots and lots of triangles. Like, seriously, who needs more than 3 sides? But no, we're stuck with 3, 4, and 5. Joy.
θ = ∠ - The most basic unit of trigonometry, an angle is like a slice of pizza. You got it? Slice. Like, a slice of pizza.
θ = ∠ = 180° - 90°
Now you know the secret to trig. Angles are just slices of pizza. Don't tell anyone.