If f(x)=x3+xf(x) = x^3 + xf(x)=x3+x, find xxx such that the slope of the tangent line is 444.
x=1x = 1x=1
x=−1x = -1x=−1
x=1x = 1x=1 and x=−1x = -1x=−1
x=2x = 2x=2