SOLUTION: i have been trying for 3 days to figure these out and can not come up with a solution. If anyone could please take the time to help me and show an example of how to do these I woul

Question 139795: i have been trying for 3 days to figure these out and can not come up with a solution. If anyone could please take the time to help me and show an example of how to do these I would be forever grateful. These are on a practice test, the real test is Monday.
A ball is thrown vertically upward with an initial velocity of 160 feet per second. The distance in feet of the ball from the ground after 1 second is s=160t - 160t^2. For what is the interval of time is the ball less than 336 feet above the ground (after it is tossed until it returns to the ground)
2. Use the compound interest formulas A=P(1 +r/n)^nt and A =P^ert to solve.
Suppose you have 9000 dollars to invest. Which investment yields the greater return over 5 years: 6.25% compounded continuously or 6.3% compounded semi annually?
3. Graph the polynomial function f(x) = -6x^4 + 9x^3
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
1.A ball is thrown vertically upward with an initial velocity of 160 feet per second. The distance in feet of the ball from the ground after 1 second is s =160t - 160t^2. For what is the interval of time is the ball less than 336 feet above the ground (after it is tossed until it returns to the ground)
:
I think the equation for this type of problem would be s = 160t - 16t^2:
:
Find the interval above 336 ft
Arrange as a quadratic equation
-16t^2 + 160t < 336
-16t^2 + 160t - 336 > 0
Simplify and change the signs, divide equation by -16
+t^2 - 10t = 21 = 0
Factor
(t-7)(t-3) = 0
t = 7; t = 3
Here is the graph of the equation y = -16t^2 + 160t
You can see the ball will be above 336 ft during the 4 sec interval between 3 sec and 7 sec.

You can also see that the ball will be less than 336 ft during the intervals
0 to 3 sec
7 to 10 sec
:
:
2.Use the compound interest formulas A=P(1 +r/n)^nt and A =P^ert to solve.
Suppose you have 9000 dollars to invest. Which investment yields the greater return over 5 years: 6.25% compounded continuously or 6.3% compounded semi annually?
:
Find the interest compounded semi-annually at 6.3% for 5 years
A = 9000 * (1 + .063/2)^(2*5)
A = 9000 * (1.0315)^10; use a calc
A = 9000 * 1.363617
A = 12,272.55
:
Find it a continuous interest after 5yrs at 6.25%:
Here I think the continuous interest formula should be P*e^rt
A = 9000 * e^(.0625*5); use a calc
A = 9000 * 1.366838
A = 12,301.54
:
:
3. Graph the polynomial function f(x) = -6x^4 + 9x^3:
If you factor this, it will give you a range of the values of x to plot
-3x^3(2x - 3)= 0
So you have x = 0 and x = +1.5, so plot this from -1 to + 2 at .5 intervals
x | y
-------
-1 | -15
-.5| -1.5
0 | 0
+.5|+.75
+1 |+3
1.5| 0
2 |-24
:
Your graph should look like this:

:
Hope this helps you out.
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