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Isabella is playing with her yo-yo. The vertical distance 
Y (in 
cm ) between the yo-yo and her hand 
t seconds after she first spins it out is modeled by the following function. Here, 
t is in radians.

Y(t)=40 cos((2pi)/(3)t)-71
How long does it take the yo-yo to fall all the way down from its peak, and then rise up to a vertical distance of 
-80cm ?
Round your final answer to the nearest tenth of a second.
seconds
[Trigonometric identity reference sheet]

Isabella is playing with her yo-yo. The vertical distance Y Y (in cm \mathrm{cm} ) between the yo-yo and her hand t t seconds after she first spins it out is modeled by the following function. Here, t t is in radians.\newlineY(t)=40cos(2π3t)71 Y(t)=40 \cos \left(\frac{2 \pi}{3} t\right)-71 \newlineHow long does it take the yo-yo to fall all the way down from its peak, and then rise up to a vertical distance of 80 cm -80 \mathrm{~cm} ?\newlineRound your final answer to the nearest tenth of a second.\newline\square seconds

Full solution

Q. Isabella is playing with her yo-yo. The vertical distance Y Y (in cm \mathrm{cm} ) between the yo-yo and her hand t t seconds after she first spins it out is modeled by the following function. Here, t t is in radians.\newlineY(t)=40cos(2π3t)71 Y(t)=40 \cos \left(\frac{2 \pi}{3} t\right)-71 \newlineHow long does it take the yo-yo to fall all the way down from its peak, and then rise up to a vertical distance of 80 cm -80 \mathrm{~cm} ?\newlineRound your final answer to the nearest tenth of a second.\newline\square seconds
  1. Given Function: We have the function Y(t)=40cos(2π3t)71Y(t) = 40 \cos\left(\frac{2\pi}{3}t\right) - 71. We need to find tt when Y(t)=80Y(t) = -80.
  2. Set Equation: Set the equation 80=40cos(2π3t)71-80 = 40 \cos\left(\frac{2\pi}{3}t\right) - 71.
  3. Isolate Cosine Term: Add 7171 to both sides to isolate the cosine term: 80+71=40cos(2π3t)-80 + 71 = 40 \cos\left(\frac{2\pi}{3}t\right).
  4. Simplify Equation: Simplify the left side: 9=40cos(2π3t)-9 = 40 \cos\left(\frac{2\pi}{3}t\right).
  5. Divide by 4040: Divide both sides by 4040 to solve for cos(2π3t)\cos\left(\frac{2\pi}{3}t\right): 940=cos(2π3t)-\frac{9}{40} = \cos\left(\frac{2\pi}{3}t\right).
  6. Calculate Value: Calculate the value of 940-\frac{9}{40}: 940=0.225-\frac{9}{40} = -0.225.
  7. Inverse Cosine Function: Use the inverse cosine function to find (2π/3)t(2\pi/3)t: (2π/3)t=cos1(0.225)(2\pi/3)t = \cos^{-1}(-0.225).
  8. Calculate (2π3)t(\frac{2\pi}{3})t: Calculate (2π3)t(\frac{2\pi}{3})t using a calculator: (2π3)t1.772(\frac{2\pi}{3})t \approx 1.772 (radians).
  9. Solve for t: Solve for t by multiplying both sides by 32π\frac{3}{2\pi}: t1.772×(32π)t \approx 1.772 \times \left(\frac{3}{2\pi}\right).
  10. Final Calculation: Calculate tt: t0.8t \approx 0.8 seconds.

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