How to Derive the Quadratic Formula: 8 Steps
The quadratic formula is a powerful tool for solving quadratic equations. It provides a systematic approach that can be used to find the roots of any quadratic equation in the form ax^2 + bx + c = 0. In this article, we’ll break down the process into eight steps to help you understand and derive the quadratic formula easily.
Step 1: Write down the general form of a quadratic equation.
A quadratic equation is an equation of degree 2, and its general form is:
ax^2 + bx + c = 0
Here, a, b, and c are constants, and x is the variable.
Step 2: Use the technique called “completing the square.”
To derive the quadratic formula, we’ll employ a technique known as “completing the square,” which involves rewriting our equation in perfect square trinomial form. This will make it easier to solve for x.
Step 3: Divide both sides by ‘a.’
To begin completing the square, divide both sides of your equation by ‘a’ so that your leading coefficient (the coefficient of x^2) is 1:
x^2 + (b/a)x + (c/a) = 0
Step 4: Isolate x terms on one side.
Now, move the constant term (c/a) to the other side of your equation:
x^2 + (b/a)x = -(c/a)
Step 5: Complete the square.
Add a value ‘k’ on both sides of your equation that will complete the square on the left-hand side:
x^2 + (b/a)x + k = -(c/a) + k
The value of k is equal to half of (b/a)^2:
k = ((b/2a))^2
Step 6: Re-write your equation in perfect square trinomial form.
Your equation should now be in perfect square trinomial form:
(x + b/2a)^2 = b^2/(4a^2) – (c/a)
Step 7: Solve for ‘x.’
Take the square root of both sides of your equation:
x + b/(2a) = ± √(b^2 – 4ac) / (2a)
Now, isolate x by moving the term ‘b/(2a)’ to the other side:
x = -b/(2a) ± √(b^2 – 4ac) / (2a)
Step 8: Simplify.
Finally, simplify your expression by combining the parts with the common denominator:
x = (-b ± √(b^2 – 4ac)) / (2a)
Congratulations! You’ve derived the quadratic formula. Now, you can use this formula to solve any quadratic equation in the form ax^2 + bx + c = 0. Simply plug in the coefficients ‘a’, ‘b’, and ‘c’ into the formula and solve for ‘x.’