## anonymous 4 years ago Oil spilled from a ruptured tanker is spreading in a circular pattern. If the radius of the circle is increasing at the constant rate of 1.5 feet per second, how fast is the area of the spill increasing when the radius of the spill is 42 feet?

1. goformit100

use speed time formula...

2. anonymous

I've never heard of that.

3. anonymous

related rates right?

4. anonymous

Yeah, related rates.

5. anonymous

$$A=\pi r^2$$ and so $$A'=2\pi rr'$$

6. anonymous

you are told $$r'=1.5$$ and $$r=42$$ plug in the numbers and get $$A'$$ in one step

7. anonymous

wow, that was easy. I'm terrible at these.

8. goformit100

@bloodrain

9. anonymous

yeah, i have to admit that one was real easy they get harder

10. anonymous

:(

11. anonymous

well only the formulas get harder to figure out, i am willing to bet that you knew the formula for the area of a circle

12. anonymous

yeah, I was just thinking like A=pi(r^t/1.5)^2 then I was super confused

13. anonymous

That made absolutely no sense to me.

14. anonymous

The minute hand on a watch is 8mm long and the hour hand is 4 mm long. How fast is the distance between the tips of the hands changing at one o'clock? THat's the hardest one I have done myself.

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