Given below are some functions of x and t to represent the displacement (transverse or longitudinal) of an elastic wave. State which of these represent (i) a travelling wave, (ii) a stationary wave, or (iii) none of all

(a) It represents a stationary wave in harmonic functions of x and t are contained separately in the equation.

(b) It cannot represent any type of wave.

© It represents a progressive travelling harmonic wave.

(d) This equation is sum of two functions each representing a stationary wave. Therefore, it represents superposition of two stationary waves