The height in metres of a projectile launched from the top of a building is given by: h(t) = -5t^2 + 20t +15, where t is the time in seconds since it was launched. When is the projectile at an altitude lower than 30m?
I've been stuck on this questions for a while now. I graphed it and I know that at 3 seconds it is at a height of 30m, and at 4 seconds it is at a height of 15m. I am not sure how to show this other than a graph. Any suggestions?

Question

The height in metres of a projectile launched from the top of a building is given by: h(t) = -5t^2 + 20t +15, where t is the time in seconds since it was launched. When is the projectile at an altitude lower than 30m?
I've been stuck on this questions for a while now. I graphed it and I know that at 3 seconds it is at a height of 30m, and at 4 seconds it is at a height of 15m. I am not sure how to show this other than a graph. Any suggestions?

anonymous · Answer

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