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Khan Academy
Khan Academy: Find a Missing Side Length When Given the Perimeter
In this exercise, students will learn how to find the length of one side of a polygon when the perimeter is given. Students receive immediate feedback and have the opportunity to watch a tutorial video, get hints, and try questions...
Illustrative Mathematics
Illustrative Mathematics: 8.g Area of a Trapezoid
Eighth graders are given various dimensions of a trapezoid and are asked to find its area. This requires them to use the Pythagorean Theorem and to decompose the trapezoid into other polygons. Aligns with 8.G.B.7.