x^2+18x=9 solve quadradic

Question

x² + 18x=9 solve quadratic for x

Answer 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:

http://www.purplemath.com/modules/quadform.htm

Answer 2

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