Deriving the Quadratic Formula Complete the square!
The Quadratic Formula The quadratic formula is give you the solutions to ax2 + bx + c = 0 in terms of a, b, and c. The formula: Where did this formula come from? The following slides will show how it’s derived.
Derivation Begin with ax2 + bx + c = 0 . Divide both sides of the equation by a to get x2 + (b/a)x + (c/a) = 0. Subtract c/a from both sides of the equation. x2 + (b/a)x = -c/a
Derivation Continued We have x2 + (b/a)x = -c/a. We want to complete the square on the left side so that we can solve for x. To complete the square, we need to add to both sides of the equation. This gives us
Derivation Continued Notice that is in the form x2+2yx+y2, as we intended. We can factor this as (x+y)2, so we have Now let’s solve for x.
Derivation Continued
Derivation Continued
Derivation Finale