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Solution 2.3:1a

From Förberedande kurs i matematik 1

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(Ny sida: {{NAVCONTENT_START}} <center> Bild:2_3_1a.gif </center> {{NAVCONTENT_STOP}})
Current revision (13:22, 26 September 2008) (edit) (undo)
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If we consider the rule
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<center> [[Bild:2_3_1a.gif]] </center>
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{{Displayed math||<math>(x-a)^{2} = x^{2}-2ax+a^{2}</math>}}
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and move <math>a^{2}</math> over to the left-hand side, we obtain the formula
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{{Displayed math||<math>(x-a)^{2}-a^{2} = x^{2}-2ax\,\textrm{.}</math>}}
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With the help of this formula, we can rewrite (complete the square of) a mixed expression <math>x^{2}-2ax</math> to a obtain a quadratic expression, <math>(x-a)^{2}-a^{2}</math>.
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The expression <math>x^{2}-2x</math> corresponds to <math>a=1</math> in the formula above and thus
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{{Displayed math||<math>x^{2}-2x = (x-1)^{2}-1\,\textrm{.}</math>}}

Current revision

If we consider the rule

(xa)2=x22ax+a2

and move a2 over to the left-hand side, we obtain the formula

(xa)2a2=x22ax.

With the help of this formula, we can rewrite (complete the square of) a mixed expression x22ax to a obtain a quadratic expression, (xa)2a2.

The expression x22x corresponds to a=1 in the formula above and thus

x22x=(x1)21.