Before a football game, a coin toss is used to determine which team will kick off. The height h (in feet) of a coin above the ground t seconds after being flipped up into the air is given by the following equation.

Question

h = -16t2 + 34t + 15.
How long does a team captain have to call heads or tails if it must be done while the coin is in the air?
seconds

Answer 1

Ask for what t is -16t^2 + 34t + 15 = 0? Use the usual quadratic formula for that one:
x = (-b +/- sqrt(b^2 - 4ac)) / 2a
sqrt(b^2 - 4ac) = 46, so the answer is either a negative number or 80/32 = 10/4 = 2.5. So that's the answer: two and a half seconds.