Finding and Interpreting Key Features of Quadratics
Algebra

Tutor: None Selected  Time limit: 1 Day 
An object is launched from a platform. Its height in meters, yyy, is dependent on time in seconds after launch, xxx, and can be modeled with the function y=−5(x+1)(x−9) How many seconds after launch will the object hit the ground? ___seconds What is the maximum height that the object will reach? ___meters How many seconds after being launched will the object reach its maximum height? ___seconds What is the height of the object at the time of launch? ___meters
1To know how many seconds after launch the object will hit the ground, we have to solve the equation
y(x)=0 so x=1 or x=9. The only possible answer is x=9 seconds as we remove the negative solution because x (time) is positive.
answer : 9 seconds.
2  You have to find the maximum of the function y(x)=5(x+1)(x9)=5(x^28x9)
y'(x)=5(2x8). The maximum value is obtained for x as y'(x)=0 so x=4. to find the maximum height, we just have to calculate y(4)=125
answer : 125 meters
3  Previously we calculated the value for x where y(x) is maximum. x=4. This is the number of seconds after beeing lauched where the object reach its maximum height.
answer : 4 seconds
4 To know the height of the object at the time of launch, we just have to calculate y(0). y(0) is the height of the object at x=0 or in other words at time of launch. y(0)=45
answer : 45 meters.
If you need something else, don't hesitate.
Secure Information
Content will be erased after question is completed.