Đáp án:
7D
8B
9D
10D
Giải thích các bước giải:
Câu 7:
`f(x)=x^4-10x^2-4` trên `[0;9]`
`f'(x)=4x^3-20x`
`f'(x)=0 ⇒` \(\left[ \begin{array}{l}x=\sqrt{5}\ \in [0;9]\\x=0\ \in [0;9]\\x=-\sqrt{5}\ \notin [0;9]\end{array} \right.\)
Ta có:
`f(0)=-4`
`f(\sqrt{5})=-29`
`f(9)=5747`
Vậy `min_{[0;9]} f(x)=-29, max_{[0;9]} f(x)=5747`
Câu 8:
`f(x)=x^4-12x^2-4` trên `[0;9]`
`f'(x)=4x^3-24x`
`f'(x)=0 ⇒` \(\left[ \begin{array}{l}x=\sqrt{6}\ \in [0;9]\\x=0\ \in [0;9]\\x=-\sqrt{6}\ \notin [0;9]\end{array} \right.\)
Ta có:
`f(0)=-4`
`f(\sqrt{6})=-40`
`f(9)=5585`
Vậy `min_{[0;9]} f(x)=-40, max_{[0;9]} f(x)=5585`
Câu 9:
`f(x)=x^4-10x^2-2` trên `[0;9]`
`f'(x)=4x^3-20x`
`f'(x)=0 ⇒` \(\left[ \begin{array}{l}x=\sqrt{5}\ \in [0;9]\\x=0\ \in [0;9]\\x=-\sqrt{5}\ \notin [0;9]\end{array} \right.\)
Ta có:
`f(0)=-2`
`f(\sqrt{5})=-27`
`f(9)=5749`
Vậy `min_{[0;9]} f(x)=-27, max_{[0;9]} f(x)=5749`
Câu 10:
`f(x)=x^4-12x^2-1` trên `[0;9]`
`f'(x)=4x^3-24x`
`f'(x)=0 ⇒` \(\left[ \begin{array}{l}x=\sqrt{6}\ \in [0;9]\\x=0\ \in [0;9]\\x=-\sqrt{6}\ \notin [0;9]\end{array} \right.\)
Ta có:
`f(0)=-1`
`f(\sqrt{6})=-37`
`f(9)=5588`
Vậy `min_{[0;9]} f(x)=-37, max_{[0;9]} f(x)=5588`
