Problem

Problem

Let F(x)=1+f(x)+(f(x))2+(f(x))3F(x) = 1 + f(x) + (f(x))^2 + (f(x))^3 , where f(x)f(x) is an increasing differentiable function and F(x)=0F(x) = 0 has a positive root, then a. F(x)F(x) is an increasing function b. F(0)≤0F(0) \le 0 c. f(0)≤−1f(0) \le -1 d. F′(0)>0F'(0) > 0

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