Let f(a)=minf(x)=- 1, then f'(a)=0. Where f(x) is x=a, the second-order Taylor formula is f (x) = f (a)+f' (a)+f' (r)/. * (x-a) 2 r belongs to (a, x)x=0, where f (0) =-1+f'' (x1)/2! * a 2 means f'' (x 1) = 2/a 2x = 1 means f (1) =-1+f'' (x2)/2! * (1-a) 2 means f'' (x2) = 2/( 1-a) 2 If 0