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Solution 2.3:1d

Revision as of 14:06, 26 September 2008 by Tek (Talk | contribs)

(diff) ←Older revision | Current revision (diff) | Newer revision→ (diff)

We apply the standard formula for completing the square,

x2+ax=

x+2a

2−

on our expression and this gives

x2+5x=

x+25

2−

x+25

2−425.

The whole expression becomes

x2+5x+3=

x+25

2−425+3=

x+25

2−425+412=

x+25

2+412−25=

x+25

2−413.

A quick check shows that we have calculated correctly

x+25

2−413=x2+2

2−413=x2+5x+425−413=x2+5x+412=x2+5x+3.