Given:
[tex]h=-3t^2+147[/tex]
Required:
We need to find the number of seconds will the plane be at a height of 20.25 feet.
Explanation:
Substitute h = 20.25 in the equation.
[tex]20.25=-3t^2+147[/tex]
Subtract 147 from both sides of the equation.
[tex]20.25-147=-3t^2+147-147[/tex]
[tex]-126.75=-3t^2[/tex]
Divide both sides of the equation by -3.
[tex]\frac{-126.75}{-3}=\frac{-3t^2}{-3}[/tex]
[tex]42.25=t^2[/tex]
Take square root on both sides.
[tex]\pm\sqrt{42.25}=\sqrt{t^2}[/tex]
Time is of positive value.
[tex]\sqrt{42.25}=t[/tex]
[tex]6.5=t[/tex]
Final answer:
After 6.5 seconds the plane will be at a height of 20.25 feet.
