Area of common shapes and circles

Area formulas for rectangles, triangles, trapeziums and circles — and why the triangle formula has a half in it.

Dakika 1 za kusomaImesasishwa 18 Oktoba 2026Na Sumzo teamImekaguliwa na Sumzo team

Area measures the space inside a flat shape, in square units (cm², m², …). Perimeter is the distance around the outside.

Rectangle: $A = l \times w$
Triangle: $A = \tfrac{1}{2} b h$ — half of a rectangle with the same base and height
Parallelogram: $A = b h$ (use the perpendicular height, not the slanted side)
Trapezium: $A = \tfrac{1}{2}(a + b)h$

Mfano uliotatuliwa

Area of a triangle

A triangle has base 10 cm and height 6 cm. Find its area.

Onyesha hatua za suluhisho

Jibu: 30 cm²

Imekaguliwa na injini ya hisabati ya Sumzo

C = 2\pi r,\qquad A = \pi r^2

r is the radius; the diameter is d = 2r.

Mfano uliotatuliwa

Find the circumference and area of a circle with radius 5.

Onyesha hatua za suluhisho

Jibu: Circumference $10\pi$ , area $25\pi$

Imekaguliwa na injini ya hisabati ya Sumzo