What is "in circle t?

"In circle T" refers to the incircle of a triangle, which is a circle that is tangent to all three sides of the triangle. The center of this circle is called the incenter, and it is equidistant from all three sides of the triangle. The radius of the incircle is called the inradius.

The inradius of a triangle can be calculated using the formula: r = A / s where r is the inradius, A is the area of the triangle, and s is the semi-perimeter (half of the perimeter) of the triangle.

The incircle of a triangle is often used in geometry problems, as it allows for the calculation of various properties related to the triangle, such as its area, perimeter, and angles.