Learn the 3-Step Method
1Find base and height.
The height is the straight-up distance from the base to the top — not a slanted side.
2Multiply base × height.
10 × 6 = 60 — that's the surrounding rectangle.
3Halve it.
The triangle is half the rectangle: 60 ÷ 2 = 30 cm².
Worked Example
A triangular sail has a base of 4 m and a height of 7 m. Find its area.
Watch Out! Common Mistakes
Wrong! That’s the rectangle. The triangle is half: 30 cm².
Wrong! Height is the perpendicular distance from base to apex — the dashed line straight up, never the sloping edge.
Wrong! Halve once, at the end: (10 × 6) ÷ 2 = 30 cm².
⬇ Cheat Sheet
- Area = (base × height) ÷ 2.
- Height is perpendicular to the base.
- Multiply first, halve once.
- Answer in square units.
📖 Continue Your Journey
Quick summary
- Area of a triangle = (base × height) ÷ 2.
- The height is perpendicular to the base — never the slanted side.
- Multiply first, then halve exactly once.
- It works because every triangle is half its surrounding rectangle.
Frequently asked questions
What is the formula for the area of a triangle?
(Base × height) ÷ 2. A triangle with base 10 cm and height 6 cm has area 30 cm².
What counts as the height of a triangle?
The perpendicular (right-angle) distance from the base to the opposite corner — not the length of a sloping side.
Why divide by 2?
Because the triangle fills exactly half of the rectangle drawn around it — two identical triangles make the whole rectangle.
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