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As shown in the figure, the area of the rectangle is 70 square centimeters, the upper bottom of the trapezoid is 3 / 7 of the length of the rectangle, and the lower bottom is 4 / 5 of the length of the rectangle
The shadow area is about the area other than trapezoid
Let the length of a rectangle be a and the width be B, then a * b = 70
The length of the top bottom of trapezoid is 3A / 7, the length of the bottom bottom is 4A / 5, and the height is B
So the area of trapezoid is: (3a / 7 + 4A / 5) * B / 2 = 43 / 70 * AB = 43 / 70 * 70 = 43
So the shadow area is: 70-43 = 27
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