Place the square tangram piece on a flat surface. The side of the square nearest to you will become part of the bottom of the finished trapezoid  that is, the longer of the trapezoid's two parallel sides. The opposite side of the square, the one farthest from you, will form part of the top of the trapezoid, the shorter of the trapezoid's two parallel sides.
How to Make a Trapezoid Using Four Tangram Pieces
A tangram puzzle has seven pieces: two large triangles, two small triangles, a mediumsize triangle, a square and a parallelogram. To make a trapezoid using four tangram pieces, you'll need the square, the two small triangles and the parallelogram. Note that the small triangles are both right triangles, with two legs of equal length and a longer hypotenuse. Note also that the hypotenuse of each small triangle is the exact same length as one of the long sides of the parallelogram. These measurements make a fourpiece trapezoid possible.
Things You'll Need
 Tangram set
Instructions


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Take one of the small triangle pieces and place it with the triangle's right angle adjacent to the lower left corner of the square. One leg of the small triangle should be flush and even with the left side of the square; the other leg should be aligned with the bottom line of the square.


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Place the other small triangle piece on the right side of the square, in the mirror positiion of the triangle on the left side. Place this triangle so that its right angle is adjacent to the lower right corner of the square, one leg is flush and even with the right side of the square, and the other leg is aligned with the bottom line of the square. At this point, you'll have a trapezoid  but with only three pieces. The top of the trapezoid is the top line of the square; the bottom of the trapezoid is made up of the bottom line of the square and a leg of each of the triangles; and the hypotenuses of the two triangles form the slanted sides of the trapezoid.

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Place the parallelogram piece on one side of the threepiece trapezoid; which side you choose is up to you. Place the parallelogram so that one of the long sides is flush and even with the hypotenuse of the triangle on the side you choose, and the two short sides of the parallelogram are aligned with the top and bottom of the threepiece trapezoid. You now have a trapezoid made from four tangram pieces.

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Tips & Warnings
 If you can't get the parallelogram piece to fit in the last step, simply flip the parallelogram piece over. The parallelogram is the only tangram piece that fits differently depending on which side is facing up.