Question 605368
y = A*sin(Bx - C) + D


In this case, A = 3 and B = 2pi/T = 2pi/(4/5pi) = 5/2. The other values of C and D are zero.


So the equation is 


<img src="http://latex.codecogs.com/gif.latex?\Large y = 3\sin\left(\frac{5}{2}x\right)" title="x" />