class introductions

```python
class Shape:
    def __init__(self, dim1, dim2):
        self.dim1=dim1
        self.dim1=dim2
    def area(self):
        return self.dim1*self.dim2
    def perimeter(self):
        return 2*(self.dim1+self.dim2)
 
class Rectangle(Shape):
    def __init__(self, length, breadth):
        self.dim1=length
        self.dim2=breadth
        
class Square(Rectangle):
    def __init__(self,length):
        self.dim1=length
        self.dim2=length
 
class Triangle(Shape):
    def __init__(self, base, height):
        self.dim1=base
        self.dim2=height
    def area(self):
        return 0.5 * (self.dim1*self.dim2)
    
rectangle=Rectangle(3,4)
print(rectangle.area())
 
square=Square(3)
print(square.area())
 
triangle=Triangle(3,4)
print(triangle.area())
 
square=Square(5)
print(square.area())
```