Usta Bala
Raise a yurt, build a bridge, fence the yard — learn geometry with your hands. Turn shapes, measure, build and calculate.
Stage 1.1 needs no account. Sign in for more: 3 stages of every chapter are free, progress is saved
Village map
0 / 72 · Stages open in order- 1.1The first post
- 1.2The gate's angleSign-in needed
- 1.3A rectangular penSign-in needed
- 1.4How much fence?Sign-in needed
- 1.5The garden bedSign-in needed
- 1.6Fencing the gardenSign-in needed
- 1.7The square fieldSign-in needed
- 1.8A symmetric yardSign-in needed
- 2.1The bridge triangleSign-in needed
- 2.2An isosceles triangleSign-in needed
- 2.3How long is the ladder?Sign-in needed
- 2.4How high does it reach?Sign-in needed
- 2.5How tall is the poplar?Sign-in needed
- 2.6The well rimSign-in needed
- 2.7A round flowerbedSign-in needed
- 2.8Turn the fenceSign-in needed
- 3.1The barn's facesSign-in needed
- 3.2The prism's edgesSign-in needed
- 3.3Unfolding the boxSign-in needed
- 3.4Covering the roofSign-in needed
- 3.5Felt for the wallsSign-in needed
- 3.6The pyramid's slant heightSign-in needed
- 3.7How much hay fits?Sign-in needed
- 3.8A yurt for the feastSign-in needed
Important numbers
Every circle’s circumference is π times its diameter. The digits never end or repeat. Archimedes squeezed it between 3.1408 and 3.1429. 14 March is Pi Day (3.14).
The number of continuous growth. Bernoulli (1683) found it computing interest added all the time: (1 + 1/n)ⁿ → e. Euler named it. Population growth and radioactive decay both follow e.
The diagonal of a square with side 1 (Pythagoras: 1² + 1² = 2). The first known number that is not a fraction — legend says the Pythagoreans tried to hide it. An A4 sheet’s sides are in the ratio √2 too.
Split a segment so the whole is to the longer part as the longer is to the shorter — that ratio is φ. Neighbouring Fibonacci numbers 1, 1, 2, 3, 5, 8, 13… divide towards φ. Sunflower seeds and shells show it everywhere.