Learning goals: Teacher Facing Explain (in writing) how to use circles to locate the point where the sides of a triangle with known side lengths should meet. Use manipulatives to justify when it is not possible to make a triangle with three given side lengths. Use manipulatives to show that there is a minimum and maximum length the third side of a triangle could be, given the other two side lengths. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 7.7 Angles, Triangles, and Prisms, Grade 7.