1. The problem statement, all variables and given/known data 2. Relevant equations y (x,y) = 2YmSin(kx)Cos(wt) 3. The attempt at a solution I am having trouble at setting up the standing wave equation for this problem. Once I set up the equation, I know that part a b c d is just plugging in the numbers. From what I learned, I know that the standing wave equation is Y(x,y) = 2YmSin(kx)Cos(wt), this is what the textbook states. (Ym being the amplitude). I calculated k and w correctly. The equation I set up was Y(x,y) = .041Sin(kx)Cos(wt) However, the solution uses the equation Y(x,y) = -2YmCos(kx)Sin(wt). therefore, Y(x,y) = -.041Cos(kx)Sin(wt) I do not understand why there is a negative sign in front of the amplitude and why Sin and Cos is switched in the equation used by the solution. Any help or guide will be greatly appreciated, Thank you.