6

Set 15: Quadratic Equations

Explanation

Answer: A

For a projectile h(t)=−16t2+64th(t) = -16t^2 + 64t, at what times is the height 48 ft?

A.

1 second and 3 seconds

✓ Correct
B.

2 seconds

C.

1 second and 2 seconds

D.

3 seconds and 4 seconds

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Set h(t)=48h(t) = 48. 1. −16t2+64t=48-16 t^2 + 64 t = 48. 2. Divide by -16: t2−4t=−3t^2 - 4 t = -3. 3. t2−4t+3=0t^2 - 4 t + 3 = 0. 4. Factor: (t−1)(t−3)=0(t - 1)(t - 3) = 0. 5. Times: t=1t=1 and t=3t=3. Choice B is incorrect because that is the max height time. Choice C is incorrect. Choice D is incorrect.

Key Steps:

•

The correct answer is 1 second and 3 seconds

Why others are wrong:
B: Choice B is incorrect and may result from a calculation error.
C: Choice C is incorrect and may result from a calculation error.
D: Choice D is incorrect and may result from a calculation error.
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