Answer:
0.51 and 11.24 seconds.
Step-by-step explanation:
The height h of a rocket with an initial upward velocity of 188 feet per second after t seconds is modeled by the function:
[tex]h(t)=188t-16t^2[/tex]
And we want to find all values of t for which the rocket's height is 92.
So, we can set h(t) = 92 and solve for t:
[tex]92=188t-16t^2[/tex]
We can divide everything by four:
[tex]23=47t-4t^2[/tex]
Rearrange the equation:
[tex]4t^2-47t+23=0[/tex]
We can use the quadratic formula:
[tex]\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]
In this case, a = 4, b = -47, and c = 23. Substitute:
[tex]\displaystyle x=\frac{-(-47)\pm\sqrt{(-47)^2-4(4)(23)}}{2(4)}[/tex]
Evaluate:
[tex]\displaystyle x=\frac{47\pm\sqrt{1841}}{8}[/tex]
Hence, our two solutions are:
[tex]\displaystyle x=\frac{47+\sqrt{1841}}{8}\approx 11.24\text{ or } x=\frac{47-\sqrt{1841}}{8}\approx0.51[/tex]
So, the rocket reaches a height of 92 feet after 0.51 seconds and again after 11.24 seconds.
