2 story problems for algebra 2/trig

[shemer77]

Homework Statement

1) A ball is thrown straight up with an initial velocity of 80 ft/s. Using the formula h=-16t^2 + 80t, determine the interval of time in which the ball is at least 64 feet above the ground?
2) The perimeter of a rectangular garden is 60ft. The area of the garden is 209 ft^2. Set up and solve a quadratic equation to determine the dimensions of the garden

For number 1 do i just do 64=-16t^2 + 80t?

 

[symbolipoint]

Those are fun problems. Neither of them rely on Trigonometry (referring to "algebr 2/trig" in your subject name). Your #2 needs two variables, maybe like x and y for the two dimensions of the reactangle. x+x+y+y=60 and x*y=209. DO IT!

 

[HallsofIvy]

Homework Statement

1) A ball is thrown straight up with an initial velocity of 80 ft/s. Using the formula h=-16t^2 + 80t, determine the interval of time in which the ball is at least 64 feet above the ground?
2) The perimeter of a rectangular garden is 60ft. The area of the garden is 209 ft^2. Set up and solve a quadratic equation to determine the dimensions of the garden

For number 1 do i just do 64=-16t^2 + 80t?

That's the first step. Of course, since that is a quadratic equation you can expect to get 2 solutions- and the problem asks for the "interval of time in which the ball is at least 64 feet above the ground". What do the two solutions to that quadratic equation represent physically?

 

[shemer77]

1) I got 4 and 1, how is that possible?
2)I got y^2-30y-209=0 as my quadratic equation is that right?

 

[symbolipoint]

1) I got 4 and 1, how is that possible?
2)I got y^2-30y-209=0 as my quadratic equation is that right?

No. You made a sign error. You want for #2, y^2-30y+209=0,
Then you are ready to finish the solution.

 

[shemer77]

thanks, what about number 1?

 

[Mentallic]

Well do you understand what hallsofivy said? From the quadratic you concluded that the solution is x=1 and x=4. Do you know what these numbers actually represent physically for the ball in motion?