# Math Help - Quadratic Equation

1. ## Quadratic Equation

Can anyone work this hard question out for me???

1) An object is thrown form a building and the height above the ground, y is given by the equation y=40 + 80t - 5t^2 where t is the time of flight(in seconds).

b) What is the height after 4 seconds?

c) At what times is the height 120m?

2. Originally Posted by GAVREED2
Can anyone work this hard question out for me???

1) An object is thrown form a building and the height above the ground, y is given by the equation y=40 + 80t - 5t^2 where t is the time of flight(in seconds).

b) What is the height after 4 seconds?

c) At what times is the height 120m?
For b) just plug in $t=4$

For c) solve the equation

$120=40+80t-5t^2 \iff 5t^2-80t+80=0 \iff t^2-16t+16=0$

can you finish from here