The method of completing square is still a long method for solving the quadratic equation, so to make calculation further short and easier, a formula is developed by the mathematician to solve quadratic equation, called **quadratic formula**.

In order to derive quadratic formula, the method of completing square is used. This is given below

Write the equation in standard form

where

Shift constant term on RHS, we get

Make the coefficient of as divide the equation by

Adding on both sides, we get

Taking square root both sides, we get

This is the quadratic formula.

__Example__:

Solve the equation by quadratic formula

__Solution__:

Write the equation in standard form

Let, ,

Using quadratic formula, we get

Either or