The base diameter of a cyclinder is equal to its height. If the total surface area of the cylinder is 54 π cm^2, find its base radius and volume.
(Give your answers in term of π if necessary.)
The mass m g of a radioactive substance after t years s given by m = 6(2)^-0.19t.
(a) Find the mass of the substance after 3 years.
(b)At least how many years later will the mass of the substance be less than 1/20 of its current mass? (Give your answercorrect to the nearest integer.)
更新1:
我也是計得這答案,∴At least 37 years.,仁但正確答案是23years.