Question 645107
It has been estimated that 1000 curies of a radioactive substance introduced
 at a point on the surface of the open sea would spread over an area of
 90,000 km2 in 90 days.
 Assuming that the area covered by the radioactive substance is a linear
 function of time t and is always circular in shape, express the radius r
 (in km) of the contamination as a function of t (in days).
:
Find the radius of a circular area of 90000 sq/km (as you apparently did)
{{{pi*r^2}}} = 90000
{{{r^2}}} = {{{90000/pi}}}
r = {{{sqrt(28648)}}}
r = 169 km is the radius of the substance in 90 days
:
r(t) = {{{169/90}}}t would be the equation