We know that at that instant {{MATH_56}} and {{MATH_57}}. We now {{CMD_58}}evaluate{{CMD_59}} the two equations at the instant when {{MATH_60}}. {{MATH_61}} From the first equation we get that {{ENV_62}} Using this result and the equation on the right, we get, at the instant when {{MATH_63}}, {{ENV_64}} Hence, the area is expanding at a rate of {{MATH_65}} {{MATH_66}} at the instant when {{MATH_67}} m. {{CMD_68}} {{CMD_69}}