Formulas
Area of a rectangle
Length x width
Inscribed angle
Arc/2
Perpendicular lines
Lines that touch to form a 90o angle
Area of a triangle
height(base1 + base2)/2
Exterior angle
(big - small)/2
Parallel lines
Two lines that don't intersect
Area of a circle
π(r)2
Interior angle
(Arc1 + arc2)/2
Obtuse angle
An angle with a measure more than 90o
Midpoint
x1 + x2/2, y1 + y2/2
Arc length
length/2πr = angle/360
Acute angle
An angle with a measure less than 90o
Surface area of a cylinder
2πrh + 2πr2
Area sector
Sector/πr2 = Angle/360
Supplementary angles