sir,how we can solve constraint equation easily?If possible sir, please give an example.

A constraint equation is a relation that has to be satisfied while solving a problem. It varies from problem to problem. For example, while studying the motion of Atwood's machine, the length of the string remains constant. So, the sum of length of the two parts of the string on either side of the pulley would remain constant. This would serve as the constraint equation for the problem.