Скачать или смотреть How to draw the circumscribed and inscribed circles of a triangle

📐CIRCUMSCRIBED CIRCLE
Using the endpoints of any side of the triangle - e.g., A and B - as centres, and a radius larger than half of AB, pass arcs on both sides of the line AB. Connect the two intersection points of the arcs, 1 and 2, with a straight line. In a similar manner construct the perpendicular bisector of one other side of the triangle. The two bisectors will meet at point T. Using T as a centre and TA, TB, or TC as a radius, draw the required circle. This method can pass a circle through any three points, not on the same straight line.

📐INSCRIBED CIRCLE
Using an arbitrary radius and any of the triangle's vertices as a centre- e.g., A-draw an arc which cuts the two sides of the triangle forming the angle. Draw two arcs of the equal radius using these two intersection points 1 and 2 as centers. Draw line Aa to the intersection point a of the two arcs, and extend the line past a. Similarly, construct the angle bisector of one other angle: the two bisectors will meet at a point t. From t, draw a line perpendicular to any side and draw the required circle, using this distance as a radius and t as a centre.