When two waves of frequencies 9 Hz and 11 Hz superpose, they produce beats. The beat frequency is the difference between the two frequencies: $fb=|f_1-f_2|=|11-9|=2Hz$. This means the amplitude of the resultant wave modulates (increases and decreases) 2 times per second. The wave pattern should show a high-frequency carrier wave (average frequency 10 Hz) whose amplitude is slowly varying at 2 Hz.

Final Answer: The figure showing a wave with a fast oscillation whose amplitude pulsates slowly at a 2 Hz rate.