First draw a sketch according to the meaning of the question, then we know that the general form of trigonometric function is y=Asin(wt+b)+c, and then we can calculate these parameters separately. I calculated A= 100 (equal to half the maximum minus the minimum) and w=π/ 12(t stands for month, six months is half a cycle, so it is.

πt/ 12)+800, after getting the exact function expression, you can draw it yourself. Don't tell me you can't draw it, hehe.