Triangle Maths

Drag three points and watch the geometry follow. Triangle Maths draws a triangle from three points you move with your finger, together with the circle through all three corners, the circle that fits inside it, and the three angle bisectors. Nothing is fixed: move a point and every line, circle and number is worked out again. WHAT IT SHOWS • The circumcircle, the one circle through P, Q and R, and its centre O. • The incircle, the largest circle that fits inside the triangle, and its centre I where the three angle bisectors meet. • J, K and M, the points where the incircle touches each side. • The angle at each corner, the three side lengths, the area, and both radii. • Coordinates for every point, measured from the origin. HOW YOU USE IT • Drag P, Q and R anywhere on the plane. • Or tick "Keep P, Q, R on one circle" and slide them around a single circle, the way the first version of this app worked. • Zoom the plane in and out with the scale control. • Turn coordinates, angle bisectors, perpendiculars and the grid on or off. • Choose a theme: Paper, Dark or Blueprint. • Put the three points in a line and see what happens: there is no circle through them, and the app says so rather than showing a number. Everything is worked out on your iPhone. There is no account, no sign-in, no internet connection and no data collection of any kind, so it works in airplane mode. Rebuilt from the ground up for modern iPhones, replacing the 2015 version.