Solving quadratics can be difficult. Completing the square is one method for solving a quadratic equation. A quadratic equation can also be solved by factoring, using the square roots, or using the quadratic formula. The cool thing is that solving quadratic equations by completing the square will always work when solving quadratic equations, and the technique is a good tool to have in your math tool belt.
How Do You Complete the Square?
This video is brought to you courtesy of dangarbo10 (YouTube)
Divide through by 4 to bring 1st term to x^2
x^2 + 3/4x + 0 = 6/4
Take half of the coefficient (don’t forget the sign!) of the x-term, and square it. Add this square to both sides of the equation.
x^2 + 3/4x + (3/8)^2 = 6/4 + (3/8)^2
Simplify
x^2 + 3/4x + 9/64 = 6/4 + 9/64
Place into standard form
(x + 3/8)^2 = 96/64 + 9/64
Combine Like terms
(x + 3/8)^2 = 105/64
Square-root both sides, remembering the “±” on the right-hand side. Simplify as necessary.
x + 3/8 = ±√105/8
Solve for x
Remember that the “±” means that you have two values for x.
x = -3/8 + √105/8
x = -3/8 – √105/8
Simplifying
4x^2 + 3x + -6 = y
Isolate the 1st 2 terms:
4x^2 + 3x + 0 = 6
Divide through by 4 to bring 1st term to x^2
x^2 + 3/4x + 0 = 6/4
Take half of the coefficient (don’t forget the sign!) of the x-term, and square it. Add this square to both sides of the equation.
x^2 + 3/4x + (3/8)^2 = 6/4 + (3/8)^2
Simplify
x^2 + 3/4x + 9/64 = 6/4 + 9/64
Place into standard form
(x + 3/8)^2 = 96/64 + 9/64
Combine Like terms
(x + 3/8)^2 = 105/64
Square-root both sides, remembering the “±” on the right-hand side. Simplify as necessary.
x + 3/8 = ±√105/8
Solve for x
Remember that the “±” means that you have two values for x.
x = -3/8 + √105/8
x = -3/8 – √105/8
THANK YOU! This video explained this to me better in five minutes, than my algebra two teacher has in the past week!
You are very welcome.