F (0) = 0, f' (x) = e kx+kxe kx, f'(0)= 1, and the tangent equation is y = X. 。

F'(x)= e kx( 1+kx), let f'(x)>0,1+kx > 0, when k>0, x>-1/k; When k < 0, x

The increased interval is when k>0, x>-1/k; When k < 0, x

The subtraction interval is when k>0, x