Question:
A ball is dropped from a height of $18$ metres. The quadratic equation $h = -2t^2 + 18$ gives you the height, $h$ metres, of the ball, after $t$ seconds.
After how many seconds does the ball hit the ground?
What I've tried so far: I have tried rearranging the equation but that just got me to a dead end. I was thinking of tried to complete the square or factorising but I am not entirely sure. Thanks for your help.
Hint: we're given a polynomial of degree 2, with a negative constant infront of the t^2 term. What would a graph of this function look like?