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Markonan skrev:[tex]ax^2 + bx + c = 0[/tex]

[tex]ax^2 + bx = -c[/tex]

[tex]x^2 + \frac{bx}{a} = -\frac{c}{a}[/tex]

[tex]x^2 + \frac{bx}{a} + (\frac{b}{2a})^2 = -\frac{c}{a} + (\frac{b}{2a})^2[/tex]

[tex](x + \frac{b}{2a})^2 = \frac{b^2}{4a^2}-\frac{c}{a}\cdot\frac{4a}{4a}[/tex]

[tex](x + \frac{b}{2a})^2 = \frac{b^2-4ac}{4a^2}[/tex]

[tex]x+\frac{b}{2a} = \pm \sqrt{\frac{b^2-4ac}{4a^2}}[/tex]

[tex]x + \frac{b}{2a} = \pm \frac{\sqrt{b^2-4ac}}{2a}[/tex]

[tex]x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}[/tex]

QED ved direkte bevis.

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Fortegns-skriveleif