The function f(x) = –10(x)(x – 4) represents the approximate height of a projectile launched from the ground into the air as a function of time in seconds, x. How long, from launch to landing, does the projectile stay in the air?

The projectile is on the ground when its height is 0. Set the function equal to zero: −10x(x − 4) = 0, which gives x = 0 or x = 4. Since x = 0 is the launch time, it lands at x = 4, so it stays in the air for 4 seconds. The correct choice is 4 seconds.

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