Triangles and radians

Circle

Is 360°, but in radians it's 2π

Arc length

The shortest side on a pizza

= rθ (radians x radius)

Segment - Made by chords

To find this, find the area of the sector and take away the triangle made

Another formula if you want is ½r²(θ -sin θ)

Sector - A slice of circle

In degrees, it's θ/360 x πr²

But in radians it's just θ/2π x πr² which = θ/2r² = ½ θr²