The resistance R of a wire of a constant length is inversely proportional to the square of its diameter d. If the resistance of a wire 2 mm in diameter is 25 ohms, find
a) an equation connecting the resistance of the wire, R, to the diameter of the wire,d.
b) the resistance of a wire with diameter 2.5 mm
c) the diameter of a wire with a resistance of 15 ohms.