Geometry
Right-triangle area
Area of a right triangle from its two legs.
Practise →Rectangle perimeter
Perimeter of a rectangle from width + height.
Practise →Missing triangle angle
Find the third angle of a triangle.
Practise →Pythagorean hypotenuse
Find the hypotenuse of a right triangle.
Practise →Pythagorean leg
Find the other leg from the hypotenuse + one leg.
Practise →Triangle area (Heron)
Area of a triangle from its three sides via Heron's formula.
Practise →Trapezoid area
Area of a trapezoid from its parallel sides + height.
Practise →Regular polygon angle
Find an interior angle of a regular polygon.
Practise →Isosceles apex angle
Find the apex angle from a base angle (angle chasing).
Practise →Isosceles exterior angle
Chase the base angle, then the exterior angle.
Practise →Cyclic quadrilateral
Opposite angles of a cyclic quadrilateral sum to 180°.
Practise →Angle between parallels
Angle at a point between two parallel lines (auxiliary line).
Practise →Inscribed & central angle
Inscribed angle = half the central angle on the same arc.
Practise →Double isosceles chase
Chase angles through two isosceles triangles (180 − 3B).
Practise →Star point angles
The five point-angles of a 5-pointed star sum to 180°.
Practise →Two tangents to a circle
Angle between two tangents = 180° − central angle.
Practise →Incentre angle (BIC)
angle BIC = 90° + A/2 (internal bisectors).
Practise →Orthocentre angle (BHC)
angle BHC = 180° − A (altitudes).
Practise →Circumcentre angle (BOC)
angle BOC = 2A (central = twice inscribed).
Practise →Angle bisector foot
angle ADB = 90° + (C − B)/2 for the bisector from A.
Practise →