# Thread: I keep getting decimals...equation of a parabola

1. ## I keep getting decimals...equation of a parabola

The path of a ball is given by y=-1/20x^2+3x+5, where y is the height (in feet) of the ball and x is the distance (in feet) from where the ball was thrown.

a) find the maximum height of the ball.
b) which number determines the height at which the ball was thrown? does changing this value change the coordinates of the maximum height of the ball? explain

2. Originally Posted by A Beautiful Mind
The path of a ball is given by y=-1/20x^2+3x+5, where y is the height (in feet) of the ball and x is the distance (in feet) from where the ball was thrown.

a) find the maximum height of the ball.
b) which number determines the height at which the ball was thrown? does changing this value change the coordinates of the maximum height of the ball? explain
a) There are several options but since you've opsted in the Pre-algebra and Algebra I suggest first completing the square:

$\displaystyle y = -\frac{1}{20} x^2 + 3x + 5 = - \frac{1}{20} (x^2 + 60 x + 100) = \, ....$

b) Here is a hint: Height at which ball was thrown: Substitute x = 0. Therefore y = ....