图形面积小计算:双浮点型的上底、下底、高，利用（上底+下底）*高/2的公式计算梯形面积；同样，用长*宽的公式计算矩形面积。-Graphic area is small calculation: double floating-point type on the bottom, under the bottom, the high, the use of (+ down on the bottom end)* High/2 formula trapezoid area　Similarly, using the formula L* W rectangular area.