y'=(x^2+1)' * (x^3-x)+ (x^2+1) * (x^3-x)' = 2x(x^3-x)+ (x^2+1)(3x^2-1) = 2x^4-2x^2+3x^4-x^2+3x^2-1=5x^4-1
y'=(x^2+1)' * (x^3-x)+ (x^2+1) * (x^3-x)' = 2x(x^3-x)+ (x^2+1)(3x^2-1) = 2x^4-2x^2+3x^4-x^2+3x^2-1=5x^4-1