In right-angled triangles abc, the angle is CAB = 90 °, AC = 4cm.

In right-angled triangles abc, the angle is CAB = 90 °, AC = 4cm. A circle centered at point C touches line AB? What is the length of the radius of the circle?

Since the triangle ABC is rectangular, with a right angle CAB, and point C is the center of the circle, the point of tangency of the circle to the straight line AB, by the property of the tangent, is a perpendicular drawn from the center of the circle of the straight line.

This perpendicular is the AC leg, then R = AC = 4 cm.

Answer: The radius of the circle is 4 cm.