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x^2+18x=9 solve quadradic

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2 Answers

How about factoring by completing the square:
 
   X2 + 18X =9
 
   X^2 + 2 ( 9X ) + 81 - 81 = 9
 
  ( X + 9 ) ^2  = 90
 
  ( X + 9 ) = ±√90
 
   X = - 9 ±3 √10
 
 The quadratic formula derives from factoring by completing the square of aX^2 + bX + c