x^2 - 18 + 79 = 0

Question

completing the square

 

Answer 1

If the equation is x^2 - 18x + 79 = 0

 

Completing the Square : move the number 79 on the other side of equal sign and use formula as indicated

x^2 +bx +(b/2)^2  = c + (b/2)^2

 

x^2 - 18x  (-18/2)^2 = -70 + (-18/2)^2

x^2 - 18x + 81 = -79 + 81

x^2 - 18x + 81 = 2

(x - 9) (x - 9) = 2

(x - 9)^2 = 2

 

Now solve for x by applying square root

 

√(x-9)^2 = ±√(2)

 

x-9 = ±√(2)

  +9    +9

 

x = 9 ± √(2)