Related Rates:
If oil spilled from a ruptured tanker spreads in a circle at a rate of 6mi^2 /hr, then how fast is the radius of the circle increasing when the area is 9mi^2? I really need help setting this up correctly.

Question

Related Rates:
If oil spilled from a ruptured tanker spreads in a circle at a rate of 6mi^2 /hr, then how fast is the radius of the circle increasing when the area is 9mi^2?      I really need help setting this up correctly.

anonymous · Answer

$$A(r)=\pi r^2$$
$$A'(t)=2\pi r r'(t)$$

anonymous · Answer

you are told that 
$$A'(t)=6$$ and that 
and you want 
$$r'(t)$$ when 
$$A=9$$ solve for r from the first equation and then plug in to second to find 
$$r'(t)$$

anonymous · Answer

oh awesome I had actually chosen the right formulas for once.

anonymous · Answer

congrats!

anonymous · Answer

now if I could just stop second guessing myself.

anonymous · Answer

thanks for the help.

anonymous · Answer

yw

amistre64 · Answer

and they wonder why no work gets done ...