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# Help!

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The equation  describes the height (in feet) of a projectile  seconds after it is launched from the surface of Mars at  feet per second. In how many seconds will the projectile first reach  feet in height? Express your answer as a decimal rounded to the nearest tenth.

Aug 27, 2022

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y=-6t^2+43t

In how many seconds will the projectile first reach 77 feet in height?

Hello Guest!

$$77=6t^2+43t\\ -6t^2+43t-77=0\ |\ /(-6)\\ t^2-\frac{43}{6}+\frac{77}{6}=0\\ t=\frac{43}{12}\pm \sqrt{(\frac{43}{12})^2-\frac{77}{6}}\\ \color{blue}t\in \{3.5,3.\overline 6\}$$

In 3.5 seconds will the projectile first reach 77 feet in height.

!

Aug 28, 2022