Answer:
Quadratic algorithms O(n²)
The execution time of a program is proportional to the square of the input size. Examples: insertion sort,selection sort etc.
If the input becomes big,as the time complexity is O(n²) it will take much time and it is quite senseless to wait this much time for a program.
The quadratic algorithms become impractical when-
Input> few thousands
Cubic algorithm O(n³)
The execution time of a program is proportional to the cubic of the input size.
Examples:Deeper nested iterations will result in O(N³)
If the input becomes big,as the time complexity is O(n³) it will take much time and it is quite senseless to wait this much time for a program.
The cubic algorithms become impractical when-
Input<few hundreds