Not all things with four sides and 90 degree angles are squares or rectangles! Sometimes the angles in these 4-sided shapes are less than (or greater than) 90 degrees, causing them to have a slightly odd shape. These are called quadrilaterals and come in a few different varieties. In this tutorial, you'll learn about them. Common Core Standards: 5.G.B.3, 5.G.B.4
Do the angles in a triangle always add up to the same thing? Would I ask it if they didn't? What do we know about the angles of a triangle if two of the sides are congruent (an isosceles triangle) or all three are congruent (an equilateral)? This tutorial is the place to find out.
Common Core Standard: 8.G.A.5