全日制普通高级中学教科书(试验修订本.必修),在第90页函数应用举例中,有这样一道例题:“有一块半径为R的钢板,计划剪裁成等腰梯形ABCD的形状,它的下底是⊙O的直径,上底的端点在圆周上,写出这个梯形周长y和腰长x的函数关系式,并求出它的定义域”.图1分析:如果此问题依据所给图 A full-time ordinary high school textbook (trial revision. Compulsory), in the function application example on page 90, has such an example: "There is a steel plate with a radius of R. It is planned to be cut into the shape of an isosceles trapezoid ABCD. The bottom is the diameter of ⊙O, the end of the upper base is on the circumference, write the functional relationship of this trapezoidal perimeter y and waist length x, and find its definition domain.” Figure 1 Analysis: If this problem is based on the given Figure