SOLUTION: The graph of a parabola of the form y = x2 + bx + c crosses the y-axis at –36 and the x-axis at x = 3. At what other point does the graph cross the x-axis? A. x = –12 B. x = –9

Algebra ->  Quadratic-relations-and-conic-sections -> SOLUTION: The graph of a parabola of the form y = x2 + bx + c crosses the y-axis at –36 and the x-axis at x = 3. At what other point does the graph cross the x-axis? A. x = –12 B. x = –9      Log On


   

Question 446870: The graph of a parabola of the form y = x2 + bx + c crosses the
y-axis at –36 and the x-axis at x = 3. At what other point does
the graph cross the x-axis?
A. x = –12
B. x = –9
C. x = 9
D. x = 12
The answer is A but im not sure how to arrive at that??????
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
the y-intercept (when x=0) is -36, so this must be the value of c
___ -36 = 0^2 + b(0) + c

the x-intercept (when y=0) is 3
___ 0 = 3^2 + 3b - 36 ___ 27 = 3b ___ 9 = b

y = x^2 + 9x - 36

factoring ___ 0 = (x + 12)(x - 3)

x - 3 = 0 ___ x = 3 ___ this was given

x + 12 = 0 ___ x = -12