Four sound waves are to be sent through the same tube of air, in the same direction:

${s}_{1}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t)$

${s}_{2}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t+0.7\pi )$

${s}_{3}(x,t)=(9.00nm)\mathrm{cos}(2\pi x700\pi t+\pi )$

${s}_{4}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t+1.7\pi )$

What is the amplitude of the resultant wave?

${s}_{1}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t)$

${s}_{2}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t+0.7\pi )$

${s}_{3}(x,t)=(9.00nm)\mathrm{cos}(2\pi x700\pi t+\pi )$

${s}_{4}(x,t)=(9.00nm)\mathrm{cos}(2\pi x-700\pi t+1.7\pi )$

What is the amplitude of the resultant wave?