1, understand the properties of parallelogram. This problem contains two properties: ① two groups of opposite sides are equal; ② The sum of a group of adjacent edges is half of the circumference.

So one of the three sides is equal to 10 and the other two sides are equal to 23.

2. The essence of this test is that the opposite sides of parallelogram are equal.

Because the bottom is 24cm, the original upper bottom is 24-8= 16cm.

3. The rectangle is a special parallelogram, so the opposite sides of the rectangle are equal.

Because the upper bottom is 20cm and the lower bottom is 40cm, the maximum length of a rectangle can only be 20cm, and the height of 10cm is the width of the rectangle, so the area is equal to length × width =200cm?