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Solving Quadratic Equations: Grade 12 math

This topic covers finding solutions to quadratic equations algebraically and numerically. Students practise factorising monic and non-monic quadratics, using square roots, completing the square, and applying the quadratic formula.

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What this covers

Solving Quadratic Equations is taught in Grade 12 (age 17 to 18) as a topic to introduce. It sits in the Algebra strand.

Worked example

Solve x^2 - 5x + 6 = 0

  1. Factorise the quadratic into two brackets: (x - 2)(x - 3) = 0
  2. Set each factor to zero: x - 2 = 0 or x - 3 = 0
  3. Solve each linear equation: x = 2 or x = 3

Answer: x = 2, x = 3

Difficulty scale

The sheet generator offers five difficulty settings for this topic.

  1. Pure quadratics of the form x^2 - c = 0 with integer square roots.
  2. Monic quadratics x^2 + bx + c = 0 factorisable over integers with positive roots.
  3. Monic quadratics with mixed signs or requiring rearrangement to equal zero.
  4. Non-monic quadratics ax^2 + bx + c = 0 factorisable over integers.
  5. Equations requiring the quadratic formula or completing the square, giving surd or rounded decimal roots.

Common mistakes

  • Forgetting the negative square root when solving x^2 = k, writing only one solution.
  • Failing to rearrange the quadratic into the standard form ax^2 + bx + c = 0 before factorising.

Curriculum links

Indicative matches to Common Core State Standards. Check wording and codes against the official document.

  • Solve quadratic equations using factoring, completing the square, or the quadratic formula across various function contexts.
  • Solve systems involving a linear equation and a quadratic equation both analytically and graphically.

Sample sheet and answers

Six questions at the level's usual difficulty. Open the editor to change, add or regenerate any of them.

Solving Quadratic Equations

Grade 12 math

Qs
6
Marks
24
NameDateScore / 24
1.
Solve x2 − 1x − 2 = 0.
[4]
2.
Solve x2 + 9x + 18 = 0.
[4]
3.
Solve x2 + 8x + 16 = 0.
[4]
4.
Solve x2 − 3x − 4 = 0.
[4]
5.
Solve x2 − 49 = 0.
[4]
6.
Solve x2 + 10x + 21 = 0.
[4]

Answer key

  1. x = −1 or x = 2Factorise: (x + 1)(x − 2) = 0; So x = −1 or x = 2
  2. x = −6 or x = −3Factorise: (x + 6)(x + 3) = 0; So x = −6 or x = −3
  3. x = −4Factorise: (x + 4)(x + 4) = 0; So x = −4 or x = −4
  4. x = −1 or x = 4Factorise: (x + 1)(x − 4) = 0; So x = −1 or x = 4
  5. x = −7 or x = 7Factorise: (x + 7)(x − 7) = 0; So x = −7 or x = 7
  6. x = −7 or x = −3Factorise: (x + 7)(x + 3) = 0; So x = −7 or x = −3