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A ball is thrown in the air from a ledge. Its height in feet is represented by 
f(x) = –16(x2 – 6x – 7), where x is the number of seconds since the ball has been thrown. The height of the ball is 0 feet when it hits the ground.

How many seconds does it take the ball to reach the ground?
 

A.6
 

B.7
 

C.1
 

D.16

Respuesta :

check the picture below.

[tex] \bf \stackrel{f(x)}{0}=-16(x^2-6x-7)\implies 0=x^2-6x-7
\\\\\\
0=(x-7)(x+1)\implies x=
\begin{cases}
\boxed{7}\\
-1
\end{cases} [/tex]

it cannot be -1, because is a seconds amount after moving.

Ver imagen jdoe0001

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