A triangle is exactly half of a rectangle (or parallelogram) with the same base and height. So triangle area is base × height, then take half. The feeder skills are rectangle area and halving a number — get them warm and the triangle formula feels obvious.
Answer these 3, then press Show my path. No grade — this just points you to the right level.
1. What is 6 × 4?
2. What is half of 24?
3. A rectangle is 8 by 5. What is its area?
Take any rectangle and cut it along a diagonal — you get two equal triangles. So a triangle's area is base × height, then divided by 2 (take half). First find base × height like a rectangle, then halve it.
Your quick check picks one for you, but you can switch any time:
Level 0 Multiply, then halve — one step at a time.
A. What is 4 × 6?
4 × 6 = 24.
B. What is half of 24?
24 ÷ 2 = 12.
C. What is half of 10?
10 ÷ 2 = 5.
Level 1 Do base × height, then halve.
A. Multiply base × height: 8 × 3 = ___?
8 × 3 = 24.
B. A triangle is half of that. Half of 24 = ___?
24 ÷ 2 = 12 square units.
C. A triangle has a slanted side of 7 and a straight-up height of 5. Which number is the height?
Height is perpendicular (straight up), so it is 5.
Level 2 Stretch into full triangle area.
A. A triangle has base 10 and height 6. Find base × height ÷ 2: ___?
10 × 6 = 60, then half of 60 = 30 square units.
B. A triangle has base 9 and height 4. What is its area?
9 × 4 = 36, then half of 36 = 18 square units.
1. What is half of 36?
36 ÷ 2 = 18.
2. A triangle has base 8 and height 5. Find base × height ÷ 2: ___?
8 × 5 = 40, then half of 40 = 20 square units.
You've practiced exactly what Lesson 5-3 uses. Time to dive in.
Start Lesson 5-3 →