先看下面一个问题:例1若一个四边形的四个内角之比是3:5:5:7,试判断这个四边形的形状.解(选自学生作业)∵四边形内角和为360°,∴这个四边形各内角的度数为360°×3/20=54°,360°×5/20=90°,360°×3520=54°,360°×7/20=90°,∵90°+90°=54°+126°=180°,∴这个四边形是直角梯形.评析这道题的解答过程至少存在如下两个推理欠缺的问题:(1)没有画出解答所必需的图形.由 Consider the following question: Example 1 If the ratio of the four interior corners of a quadrilateral is 3: 5: 5: 7, try to determine the shape of this quadrilateral. Solution (from a student assignment) 和 The interior angle of the quadrilateral is 360 °, The degree of each inner corner of the quadrangle is 360 ° × 3/20 = 54 °, 360 ° × 5/20 = 90 °, 360 ° × 3520 = 54 °, 360 ° × 7/20 = 90 °, ∵90 ° + 90 ° = 54 ° + 126 ° = 180 °, ∴ This quadrilateral is a right-angled trapezoid. There are at least two problems in the solution to the problem as follows: (1) The necessary graphics are not drawn.