Completing the SquareTurning any quadratic into vertex form — and where the…10th GradeAdd and subtract (b/2)² to turn x² + bx into aperfect square, leaving the equation unchangedin value.x² + bx + (b/2)² = (x + b/2)²x² + 6x(x+3)² − 9Half of 6 is 3; 3² is 9.x² + 6x + 5 = 0(x+3)² = 4x = −1 or −5.x² − 8x + 3(x−4)² − 13Half of −8 is −4.2x² + 8x + 1factor out the 2 first2(x² + 4x) + 1, then complete inside.THE COMMON MISTAKE✗ adding (b/2)² without subtracting it✓ add AND subtract itAdding alone changes the expression's value. It must net to zero.Applying this to ax² + bx + c = 0 in general produces the quadraticformula. That is where it comes from.Completing the Squarewww.littleactivity.com

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Math · 10th Grade

Completing the Square

Turning any quadratic into vertex form — and where the quadratic formula comes from.

How to use it

Halve b, square it, add and subtract. Three moves, always in that order.

Free · print-ready PDF · US Letter and A4

Grade
10th Grade
Ages
15–16
Subject
Math
Pages
1

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