三次函数的一般形式为f(x)=ax3+bx2+cx+d(a≠0,a,b,c,d是常数),其导函数为f′(x)=3ax2+2bx+c,判别式为Δ=4b2-12ac,则函数f(x)的图像为如下几种情形:(1)当a>0且Δ<0时,f′(x)>0在x∈(-∞,+∞)上恒成立,图像如下(A); The general form of the cubic function is f (x) = ax3 + bx2 + cx + d (a ≠ 0, a, b, c and d are constants) The discriminant is Δ = 4b2-12ac, then the image of the function f (x) is as follows: (1) When a> 0 and Δ <0, f ’ + ∞), the image is as follows (A);