Area of a triangle, step by step
The triangle is half of the rectangle around it.
The question
cm²
Area of a 17 by 16 triangle
- A triangle. Two of its numbers matter and they are not the two longest lines — find them before working anything out.
- The base is the side it stands on: 17 cm.
- The height is the DASHED line — straight up from the base, at a right angle to it: 16 cm. It is not the sloping side, even though the sloping side is longer and is written right next to it.
- Now the halving. Turn a second copy of the triangle upside down against this one and the two together make a parallelogram — 17 × 16 = 272. The triangle is exactly half of it.
- So half of 272 is 136 square cm.
How it works.
- 01
A triangle. Two of its numbers matter and they are not the two longest lines — find them before working anything out.
- 02
The base is the side it stands on: 17 cm.
- 03
The height is the DASHED line — straight up from the base, at a right angle to it: 16 cm. It is not the sloping side, even though the sloping side is longer and is written right next to it.
- 04
Now the halving. Turn a second copy of the triangle upside down against this one and the two together make a parallelogram — 17 × 16 = 272. The triangle is exactly half of it.
- 05
So half of 272 is 136 square cm.