The area of a triangle is ½ × base × height.
The height must be perpendicular — straight up from the base at 90°. It's not always the slanted side. Sometimes you have to draw a dotted line from the highest point straight down to the base.
Why ½? Because any triangle is exactly half of a rectangle with the same base and height. Cut a rectangle diagonally and you get two identical triangles.
Remember
A = ½bh. The "½" comes from the fact that a triangle is half a rectangle. If you forget the formula, draw the rectangle around it.
Real World
The triangular sails on sailing boats — to find how much fabric is needed, you calculate the area using ½ × base × height.
Feeling ready?
Put this concept to work with a practice workout.