The x - intercepts of a parabola are (-5, 0) and (3, 0). What is the function of the parabola? f (x) = - 2 (x2 + 2x - 5) f (x) = - 2 (x2 + 2x - 15) f (x) = - 2 (x2 - 2x - 15) f (x) = - 2 (x2 - 2x - 5)

Question

Mathematics

Hana Carr

8 December, 17:35

The x - intercepts of a parabola are (-5, 0) and (3, 0). What is the function of the parabola? f (x) = - 2 (x2 + 2x - 5) f (x) = - 2 (x2 + 2x - 15) f (x) = - 2 (x2 - 2x - 15) f (x) = - 2 (x2 - 2x - 5)

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Jacqueline Burke · Answer 1

Just need to substitute (with some patience) x=-5 and see whether you get f (x) = 0, and x=3.

Now, a parabola is also f (x) proportional to (x+5) * (x-3) (if you know the solutions, which you do in this particular example). So: x^2 + 2*x - 15. This is the third one. The - 2 is there to confuse, any number could be there because in this example since f (x) = 0 for x=-5 and x=3, it won't change 0*number=0.