🐻 enter the geometry den

Geobear

Geometry you grab with your hands. Drag the shapes, watch the numbers obey the rules.

side/angle a side/angle b side/angle c

1 angles

An angle is just how far one arm has swung open.

Grab the pink arm and swing it. The number is the opening, in degrees. A full turn is 360°. Watch when it hits the special spots.

the angle60°

what kindacute

✋ drag the pink dot around the circle

🍯 Honey Check

name the angle

An angle of exactly 90° is called…

An angle of 140° (bigger than 90, less than 180) is…

2 the triangle rule

Bend a triangle any way you like. The three angles always add to 180°.

Drag any corner. The angles change — but their sum never does. That's the rule the whole subject leans on.

angle A—

angle B—

angle C—

the three always add upA + B + C = 180°

✋ drag any corner of the triangle

🍯 Honey Check

use the 180° rule

Two angles are 50° and 60°. The third is…

A right triangle has one 90° angle. The other two must add to…

3 pythagoras

The two little squares always fill the big one.

Drag the legs of the right triangle. The square on side a plus the square on side b always equals the square on the long side c. That's a² + b² = c².

side a3

side b4

side c5

the squares, added up

✋ drag the pink & teal dots to resize the legs

🍯 Honey Check

a² + b² = c²

Legs 3 and 4. The hypotenuse is… (9 + 16 = 25)

Legs 6 and 8. The hypotenuse is… (36 + 64 = 100)