The height of an equilateral triangle is 9 cm. Find the circumference inscribed in this triangle.

Since the triangle is equilateral, its height is also the median and bisector, which are equal in an equilateral triangle.

The center of the inscribed circle is the center of intersection of the bisectors of the triangle, and since the bisector coincides with the median, in the center of the circle they are divided in a ratio of 2/1 starting from the apex of the triangle, then R = 9 * 1/3 = 3 cm.

Then the circumference is: C = 2 * π * R = 6 * π cm.

Answer: E) The circumference is 6 * π cm.