forum.alglib.net

HI, I have some points on image. The position of points
ex: x = [100 180 200 300 400 500 600 700]
y = [100 300 500 300 100 400 500 200]

I taken sin function y = a*sin(x)+b*cos(x)+c

but my problem is, if i take directly sin(100)or sin(180)
the final fitted points(Yest) are almost same.
I think it is due to sin(theta), theta should be less than 360.If so how do i calculate sin(x)


Thank u in advance, hope of getting solution