Question

The table shows the approximate height of a projectile x seconds after being fired into the air.


Which equation models the height, y, x seconds after firing?

y = –10(x)(x – 5)
y = 10(x)(x – 5)
y = –10(x – 5)
y = 10(x – 5)

Answer 1

y = –10(x)(x – 5)

Reason: The height is a parabola that is zero at x = 0 and x = 5, so it has factors x and (x − 5). A projectile opens downward, so the leading coefficient is negative; −10x(x − 5) = −10x^2 + 50x fits.