Need help on my math final please!

Question

A stone is tossed down from a cliff at an initial velocity of 4ft per second. The distance s that the stone falls after t seconds is given by s = 4t^2 +16t. If the cliff is 884 Ft tall, in how many seconds will the stone reach the bottom of the cliff?

Answer 1

First off, since we want to know when the stone hits the ground, we'll set s = 4t^2 +16t equal to the 884 height of the cliff.

884 = 4t²+16t.

Then get everything to one side, either

0= 4t²+16t -884 or

0= -4t²-16t + 884

(Different teachers will prefer you do one or the other, but functionally, they're the same.)

If you have access to a graphing calculator, you might want to graph this now. If not, throw it into the quadratic formula.

X = negative b plus or minus the square root of b-squared minus 4ac all over two a

where a is the coefficient of the squared term (either 4 or negative 4, depending on which way you simplified), b is the coefficient of the linear term (16 or negative 16), and c is the constant term (either negative 884 or positive 884).

You should get two answers out, and we care about the positive answer, 13.