7-2 计算正五边形的面积和周长 (25分)

这道题不难，有一个坑点是Math.tan函数的参数注意单位是rad

这使得我卡了半天，又没按照题目要求写，没全对，鉴借的别人的代码，特此记录

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       import 
       
       java.
       
       text.
       
       DecimalFormat;
       
       

       
       import 
       
       java.
       
       util.
       
       Scanner;
       
       

       
       

       
       abstract 
       
       class 
       
       shape {
       
       

       
       

       
       public 
       
       abstract 
       
       double 
       
       getArea();
       
       

       
       
 
       
       public 
       
       abstract 
       
       double 
       
       getPerimeter(); 
       
       
}
       
       

       
       class 
       
       RPentagon 
       
       extends 
       
       shape{
       
       
    
       
       private 
       
       double 
       
       a;
       
       
    
       
       
    
       
       public 
       
       double 
       
       getArea() {
       
       
        
       
       
        
       
       return 
       
       5
       
       *
       
       Math.
       
       pow(
       
       a,
       
       2)
       
       /(
       
       4
       
       *
       
       Math.
       
       tan(
       
       36
       
       *
       
       Math.
       
       PI
       
       /
       
       180));
       
       
    }
       
       

       
       
    
       
       
    
       
       public 
       
       double 
       
       getPerimeter() {
       
       
        
       
       
        
       
       return 
       
       5
       
       *
       
       a;
       
       
    }
       
       
    
       
       public 
       
       RPentagon(
       
       double 
       
       a1){
       
       
        
       
       a
       
       =
       
       a1;
       
       
    }
       
       
}
       
       

       
       public 
       
       class 
       
       Main{
       
       
    
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[]
       
       args){
       
       
        
       
       DecimalFormat 
       
       df
       
       =
       
       new 
       
       DecimalFormat(
       
       "#.####");
       
       
        
       
       Scanner 
       
       in
       
       =
       
       new 
       
       Scanner(
       
       System.
       
       in);
       
       
        
       
       RPentagon 
       
       r
       
       =
       
       new 
       
       RPentagon(
       
       in.
       
       nextDouble());
       
       
        
       
       System.
       
       out.
       
       println(
       
       df.
       
       format(
       
       r.
       
       getArea()));
       
       
        
       
       System.
       
       out.
       
       println(
       
       df.
       
       format(
       
       r.
       
       getPerimeter()));
       
       
    }
       
       
}
      
      
      
      

       
       
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