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Completing the square is an algebraic technique to rewrite a quadratic ax² + bx + c in the form a(x − h)² + k. It reveals the vertex of a parabola and is used to derive the quadratic formula, solve quadratic equations, and integrate rational functions.

Trinn-for-trinn guide

  1. 1Start with ax² + bx + c
  2. 2Factor out a from the first two terms: a(x² + (b/a)x) + c
  3. 3Add and subtract (b/2a)²: a(x + b/2a)² + c − b²/4a
  4. 4Result: vertex form a(x − h)² + k where h = −b/2a, k = c − b²/4a

Løste eksempler

Inndata
x² + 6x + 5
Resultat
(x+3)² − 4
Add/subtract (6/2)²=9: x²+6x+9−4
Inndata
2x² − 8x + 3
Resultat
2(x−2)² − 5
Factor 2, complete, vertex at (2, −5)

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