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x^2+18x=9 solve quadradic

x2 + 18x=9 solve quadratic for x

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Robert A. | Certified Teacher and Engineer - Tutoring Physics, Maths, and SciencesCertified Teacher and Engineer - Tutorin...
5.0 5.0 (114 lesson ratings) (114)
1
x2 + 18x = 9
subtract 9 from both sides
1x2 + 18 x -9 = 0
 
then use the quadratic formula
x = ( -B ± SQRT( B2 - 4AC)) / 2A
 
Where A=1, B=18, C= -9
 
Can you do the arithmetic?
More help is at:
Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...
4.8 4.8 (4 lesson ratings) (4)
0
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