Area of Triangles & Special Quadrilaterals

How the lesson starts: Area of Triangles & Special Quadrilaterals

The Kite Festival
Welcome to the Kite Festival! Kai sews kites from bright fabric. Today Kai is making triangle kites. To buy the right amount of fabric, Kai needs each kite's area. The secret? Every triangle is half of a rectangle!
Half a rectangle
Cut a 10 by 6 rectangle along its diagonal. You get two matching triangles! Each one is half of 60, which is 30. That's why a triangle's area is 1/2 × base × height. In a right triangle, the two sides that make the square corner are the base and the height.
Straight-up height
Which length is the height? The height must meet the base at a square corner, like a flagpole standing straight up. This kite has a slanted side of 6, but its straight-up height is 5. The slanted side is longer, but it's not the height!