Fitting data to a curve

Xdata(.....),ydata(....., Now I want to fit this data to the curve equation a*sin(bx^2+cx+d)+e; I use curve fitting tool .ButI get very high value of sse value and large values of residues.I change start points ..Basically try every thing possible with Fit options.But still sse has not decreased..How can I best fit the data????

[Walter Roberson]

What reason do you have to expect that function will fit the data?