Posted by edward on Saturday, November 24, 2012 at 4:07am.
a circular inkblot grows at a rate of 2 sq cm per second. find the rate at which the radius is increasing after (28/11)seconds.

maths  Steve, Saturday, November 24, 2012 at 4:55am
assuming it had zero area at t=0,
a = pi r^2
da/dt = 2pi r dr/dt
2 = 2pi (28/11) dr/dt
11/(28pi) = dr/dt

maths  edward, Saturday, November 24, 2012 at 7:12am
i tried this way but answer not coming..... :/
ans is 0.25

maths  Steve, Saturday, November 24, 2012 at 10:39am
nope. I don't buy it. I think the answer lost a factor of 2 somewhere. 11/(28pi) is 0.125
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