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高中数学选择性必修 第二册(381题)


第221题



参考答案:\(g{t_0}\)


解析:


平均速度为\(\frac {Δs} {Δt}=\frac {\frac {1} {2}g{{({{t}_{0}}+Δt)}^{2}}-\frac {1} {2}g{{t}_{0}}^{2}} {Δt}=\frac {1} {2}g\frac {2{{t}_{0}}Δt+{{(Δt)}^{2}}} {Δt}=\frac {1} {2}g(2{{t}_{0}}+Δt)\)




瞬时速度为\(\mathop{\lim}\limits_{Δt\to 0}\frac {Δs} {Δt}=\mathop{\lim}\limits_{Δt\to 0}\frac {1} {2}g(2{{t}_{0}}+Δt)=g{{t}_{0}}\)









第224题


A.\(\sin 2x\)

B.\( - \sin 2x\)

C.\(2\sin 2x\)

D.\( - 2\sin 2x\)


参考答案:D


第225题


A.\({\left( {\sin \frac{\pi }{4}} \right)^\prime } = \cos \frac{\pi }{4}\).

B.已知函数\(f\left ( {x} \right )\)在\(\text{R}\)上可导,且\(f'(1) = 1\),则\(\mathop {\lim }\limits_{\Delta x \to 0} \frac{{f(1 + 2\Delta x) - f(1)}}{{\Delta x}} = 2\).

C.一质点的运动方程为\(S = {t^2}\),则该质点在\(t = 2\)时的瞬时速度是4.

D.已知函数\(f(x) = \cos x\),则函数\(y = {f^\prime }(x)\)的图象关于原点对称.


参考答案:BCD



第227题



参考答案:20


解析:


依题意,\(\frac {\Delta y} {\Delta x}=\frac {{{[2(3+\Delta x)-1]}^{2}}-{{5}^{2}}} {\Delta x}=\frac {{{(5+2\cdot \Delta x)}^{2}}-{{5}^{2}}} {\Delta x}=20+4\cdot \Delta x\)



\(y'{{|}_{x=3}}=\mathop{\lim}\limits_{\Delta x\to 0}(20+4\cdot \Delta x)=20\),所以函数\(y = {(2x - 1)^2}\)\(x = 3\)处的导数是20.







第228题



参考答案:\({f^\prime }(x) = 2x - \frac{1}{2}\);


解析:


\(\because \Delta y=f(x+\Delta x)-f(x)\)\(={(\Delta x{)}^{2}}+2x\cdot \Delta x-\frac {1} {2}\Delta x\)



\(\therefore \frac {\Delta y} {\Delta x}=2x+\Delta x-\frac {1} {2}\)



\(\therefore {{f}^{\prime }}(x)=\mathop{\lim}\limits_{\Delta x\to 0}\frac {\Delta y} {\Delta x}=2x-\frac {1} {2}\)



\({f^\prime }(1) = 2 \times 1 - \frac{1}{2} = \frac{3}{2}\)






第229题



参考答案:\(\frac{3}{2}\)


解析:


\(\because \Delta y=f(x+\Delta x)-f(x)\)\(={(\Delta x{)}^{2}}+2x\cdot \Delta x-\frac {1} {2}\Delta x\)



\(\therefore \frac {\Delta y} {\Delta x}=2x+\Delta x-\frac {1} {2}\)



\(\therefore {{f}^{\prime }}(x)=\mathop{\lim}\limits_{\Delta x\to 0}\frac {\Delta y} {\Delta x}=2x-\frac {1} {2}\)



\({f^\prime }(1) = 2 \times 1 - \frac{1}{2} = \frac{3}{2}\)







第231题


A.\((\frac {1} {e},-1)\)

B.\((e,1)\)

C.\((\sqrt {e},\frac {1} {2})\)

D.\((0,1)\)


参考答案:B






第236题



参考答案:\(f(x) = {x^3} - x + 2\);


解析:

\(f(x) = a{x^3} - ax + b\)求导得:\(f'(x) = 3a{x^2} - a\)



\(f(1)=2,f'(1)=2\),则\(\left\{ {\begin{array}{*{20}{l}} {b = 2} \\ {2a = 2} \end{array}} \right.\),解得\(a=1,b=2\)



所以\(f\left ( {x} \right )\)的解析式为\(f(x) = {x^3} - x + 2\).


第237题



参考答案:\(2x - y + 4 = 0\).

由(1)得,\(f'(x) = 3{x^2} - 1\),则\(f'(-1)=2,f(-1)=2\),

\(f\left ( {x} \right )\)在\((-1,f(-1))\)处的切线方程为\(y - 2 = 2(x + 1)\),即\(2x - y + 4 = 0\),

所以\(f\left ( {x} \right )\)在\((-1,f(-1))\)处的切线方程是:\(2x - y + 4 = 0\).


解析:

\(f(x) = a{x^3} - ax + b\)求导得:\(f'(x) = 3a{x^2} - a\)



\(f(1)=2,f'(1)=2\),则\(\left\{ {\begin{array}{*{20}{l}} {b = 2} \\ {2a = 2} \end{array}} \right.\),解得\(a=1,b=2\)



所以\(f\left ( {x} \right )\)的解析式为\(f(x) = {x^3} - x + 2\).


第238题



参考答案:\(f(x) = {x^3} + {x^2} - x + 1\);


解析:

\({f^\prime }(x) = 3{x^2} + 2ax + b\)



根据题意可得:



\(\left\{ {\begin{array}{*{20}{l}} {f(1) = 1 + a + b + c = 2} \\ {f'(1) = 3 + 2a + b = 4} \\ {f'( - 1) = 3 - 2a + b = 0} \end{array}} \right.\) ,



解得\(a=1,b=-1,c=1\)



所以\(f(x) = {x^3} + {x^2} - x + 1\)


第239题



参考答案:\(f{(x)_{\min }} = - 1\),\(f{(x)_{\max }} = 11\).

由\((1)\)知:

\({f^\prime }(x) = 3{x^2} + 2x - 1\),

令\(f'(x) = \)\((3x - 1)(x + 1) = 0\),

解得\(x = \frac{1}{3},x = - 1\),

当\(x\in \left [ {-2,-1} \right )\)时,\({f}^{\, '}\left ( {x} \right )>0\),\(f\left ( {x} \right )\)为增函数,

当\(x\in (-1,\frac {1} {3})\)时,\({f}^{\, '}\left ( {x} \right )<0\),\(f\left ( {x} \right )\)为减函数,

当\(x\in \left ( {\frac {1} {3},2} \right ]\)时,\({f}^{\, '}\left ( {x} \right )>0\),\(f\left ( {x} \right )\)为增函数,

由\(f( - 2) = - 1\),\(f( - 1) = 2\),

\(f(\frac{1}{3}) = \frac{{22}}{{27}}\),\(f(2) = 11\),

所以\(f{(x)_{\min }} = - 1\),\(f{(x)_{\max }} = 11\).



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