Perimeter & Area
Fences, tiles, and drawing shapes on a grid.
Learn with Kutty
Go one screen at a time. Press Next when you are ready. Tap 🔊 Read to me to listen.
A triangle is half of a rectangle with the same base and height.
Look: The green triangle is exactly half of the 8 × 5 rectangle: ½ × 8 × 5 = 20 cm².
✏️ Your turn!
Type your answer and press Check. Kutty will tell you if it is right.
1Base 10 cm, height 6 cm. Triangle area?
2Parallelogram: base 7 m, height 5 m. Area?
3Triangle area 24 cm², base 8 cm. Height?
! Careful!
✗Using the slanted side as the height.
✓Use the height that goes straight up.
✗Forgetting the ½.
✓A triangle is half: ½ × base × height.
See the whole lesson on one page
A triangle is half of a rectangle with the same base and height.
Rectangle area = base × height. So triangle area = ½ × base × height. The height goes straight up, not along a slanted side.
Think of it like thisCut a square sandwich corner to corner. Each triangle is half the sandwich.
- Height
- Straight up from the base, at a right angle.
Solved together
A triangle has a base of 12 cm and a height of 7 cm. Its slanted side is 10 cm. Find the area.
The height is the dashed line going straight up: 7 cm. Ignore the slanted 10 cm.
Half of base × height.
½ × 12 × 7 = 42
AnswerArea = 42 cm².
For older learners and grown-ups: a little more
A parallelogram can be cut and slid into a rectangle with the same base and height, so its area is base × height. Two copies of a triangle make a parallelogram, which is why the triangle gets the ½.
Now practise it
Kanakku makes new questions on perimeter & area every time. It shows the working and gives a hint when you are stuck.