Math basics › Geometry
Area and perimeter
The ones worth knowing
Rectangle bh. Triangle ½bh. Circle πr², circumference 2πr. Trapezoid ½(b₁ + b₂)h.
Height means perpendicular height
Not the slanted side. For an obtuse triangle the height can fall outside the triangle entirely.
Units
Area is squared, volume is cubed. If the answer is a length and your units are cm², something is wrong.