+1452 Marina solved the quadratic equation 9x^2-18x-720=0 by completing the square. In the process, she came up with the equivalent equation (x+r)^2 = s,where r and s are constants. What is s?
+9481 9x2 - 18x - 720 = 0 Divide through by 9 .
x2 - 2x - 80 = 0 Add 80 to both sides.
x2 - 2x = 80 Add (2/2)2 , which is 1 , to both sides of the equation.
x2 - 2x + 1 = 80 + 1 Factor the left side as a perfect square trinomial.
(x - 1)(x - 1) = 81
(x - 1)2 = 81
Now we have it in the form (x + r)2 = s , and we can see that s = 81 .
+9481 9x2 - 18x - 720 = 0 Divide through by 9 .
x2 - 2x - 80 = 0 Add 80 to both sides.
x2 - 2x = 80 Add (2/2)2 , which is 1 , to both sides of the equation.
x2 - 2x + 1 = 80 + 1 Factor the left side as a perfect square trinomial.
(x - 1)(x - 1) = 81
(x - 1)2 = 81
Now we have it in the form (x + r)2 = s , and we can see that s = 81 .
