Reading data in lists: Error

[Paul McGuire]

        NXD=sqrt(((y[i]-y[i-1])**2)+((x[i]-x[i-1]**2))
        NYA=x[i]-x[i-1]       < syntax error raised on this line, because
mismatched ()'s on previous line
        NYD=sqrt(((y[i]-y[i-1])**2)+((x[i]-x[i-1]**2))
        NX=NXA/NXD

-- Paul