The intensity (i) of a sound wave varies jointly as the square of its frequency (f), the square of its amplitude (a), the speed of sound (v), and the density (d) of the substance the wave is traveling through. which shows this relationship using k as the constant of proportionality? a) k = i f2a2vd b) i = k f2a2vd c) k = if2a2vd d) i = kf2a2vd