Find the two times when a projectile is at a height of 140m, if the height, h metres, after time, t seconds, is given by the expression h=40t-5t^2+80??

Question

shane_b · Answer

It's a quadratic problem...so adjust the equation so it's equal to 0 and solve it by using one of the methods for solving quadratics.

shane_b · Answer

Maybe this will help: http://www.wolframalpha.com/input/?i=solve+for+x%3A+40x-5x^2-60%3D0

anonymous · Answer

insert 140 into h=40t-5t^2+80
140=40t-5t^2+80
Now just solve the quadratic equation
140=40t-5t^2+80

anonymous · Answer

140=40t-5t^2+80
5t^2 - 40t + 140 - 80
5t^2 - 40t + 140 - 80
5t^2 - 40t + 60

Now just solve the quadratic equation
5t^2 - 40t + 60

anonymous · Answer

sweet. why did you changes the signs around???

anonymous · Answer

It is easier to work with 5t^2 than work with -5t^2

anonymous · Answer

but we could still work with -5t^2??

anonymous · Answer

Yes

anonymous · Answer

Thanks you guys and girls

anonymous · Answer

Remember though,you could still work with -5t^2 but it still needs to be converted to 5t^2. To convert it one might distrubute a -1 to converted it so it is best to just do it the way I did it.