F(x)=∫0x(t−3t2+7)dt
By the Fundamental Theorem of Calculus
F′(x)=x−3x2+7 Find the critical points of F(x)
F′(x)=0=>x−3x2+7=0
3x2−x−7=0
D=(−1)2−4(3)(−7)=85
x=2(3)1±85
x1=61−85,x2=61+85If x<61−85,F′(x)<0,F(x) decreases.
If 61−85<x<61+85,F′(x)>0,F(x) increases.
If x>61+85,F′(x)<0,F(x) decreases.
(a)The function F(x) has the local minimum at x=61−85.
(b) The function F(x) increases on
(61−85,61+85). The function F(x) decreases on
(−∞,61−85)∪(61+85,∞)
(c)
F′′(x)=(x−3x2+7)′=1−6x Find the inflection point(s)
F′′(x)=0=>1−6x=0=>x=61 If x<61,F′′(x)>0,F(x) is concave up.
If x>61,F′′(x)<0,F(x) is concave down.
The function F(x) is only concave up on (−∞,61).
The function F(x) is only concave down on (61,∞).
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