练习题[28] 代数变形

1、\(\left(1-\dfrac 12+\dfrac 13-\dfrac 14+\cdots+\dfrac{1}{2011}-\dfrac{1}{2012}\right)\div\left(\dfrac{1}{1007}+\dfrac{1}{1008}+\cdots+\dfrac{1}{2012}\right)=\)_______.

2、\(\sqrt{2+\sqrt{2+\sqrt{2+\sqrt{2+\cdots}}}}=\)_______.

3、\(\dfrac{\left(3^4+4\right)\left(7^4+4\right)\left(11^4+4\right)\cdots\left(39^4+4\right)}{\left(5^4+4\right)\left(9^4+4\right)\left(13^4+4\right)\cdots\left(41^4+4\right)}=\)_______.

4、对于任意的实数\(x,y,z\),定义运算\(\otimes\)为:\[x\otimes y=\dfrac{3x^3y+3x^2y^2+xy^3+45}{(x+1)^3+(y+1)^3-60},\]且\(x\otimes y\otimes z=\left(x\otimes y\right)\otimes z\),则\(2013\otimes 2012\otimes 2011\otimes\cdots \otimes 3\otimes 2=\)_______.

5、\(\sqrt[3]{\dfrac{\sqrt 5-1}2-\left(\dfrac{\sqrt 5-1}{2}\right)^2}=\)_______.

6、\(1+\dfrac{1}{\sqrt 2}+\dfrac{1}{\sqrt 3}+\dfrac{1}{\sqrt 4}+\cdots+\dfrac{1}{\sqrt{100}}\)的整数部分为_______.

7、已知\(x=\sqrt[3] 9+\sqrt [3] 3+1\),则\(\left(\dfrac{2}{x}+1\right)^3=\)_______.

8、已知\(f(x)=\dfrac{1}{\sqrt[3]{(x+1)^2}+\sqrt[3]{x^2+x}+\sqrt[3]{x^2}}\),则\(f(1)+f(2)+f(3)+\cdots+f(511)=\)_______.

9、已知\(x-y=6\),\(\sqrt{x^2-xy}+\sqrt{xy-y^2}=9\),则\(\sqrt{x^2-xy}-\sqrt{xy-y^2}=\)_______.

10、\(\dfrac{x}{y+z}+\dfrac{y}{z+x}+\dfrac{z}{x+y}=1\),则\(\dfrac{x^2}{y+z}+\dfrac{y^2}{z+x}+\dfrac{z^2}{x+y}=\)_______.

11、已知\(abc=1\),且\[\begin{cases}\dfrac{by}{z}+\dfrac{cz}y=a,\\\dfrac{cz}{x}+\dfrac{ax}z=b,\\\dfrac{ax}y+\dfrac{by}x=c,\end{cases}\]则\(a^3+b^3+c^3=\)_______.

12、\(abc=1\),则\(\dfrac{a}{ab+a+1}+\dfrac{b}{bc+b+1}+\dfrac{c}{ca+c+1}=\)_______.

13、已知\(a,b,c,d\)均不为\(0\),且互不相等,若\[a+\dfrac 1b=b+\dfrac 1c=c+\dfrac 1d=d+\dfrac 1a,\]则\(a^2b^2c^2d^2=\)_______.


参考答案

1、\(1\) 提示    将被除数中的\(-\dfrac{1}{2k}\)拆为\(\dfrac 1{2k}-\dfrac 1k\)即得.

2、\(2\) 提示    令原式值为\(x\),则解方程\(\sqrt{2+x}=x\)即得.

3、\(\dfrac{1}{353}\) 提示    \(x^4+4=\left(x^2+2\right)^2-(2x)^2=\left[(x-1)^2+1\right]\cdot\left[(x+1)^2+1\right]\).

4、\(\dfrac{5463}{967}\) 提示    \(x\otimes 3=9\).

5、\(\dfrac{\sqrt 5-1}{2}\) 提示    \(\dfrac{\sqrt 5-1}2\)是方程\(x^2+x-1=0\)的根,于是\(x^3+x^2-x=0\).

6、\(18\) 提示    \(\sqrt{n+1}-\sqrt{n}<\dfrac{1}{2\sqrt n}<\sqrt n-\sqrt{n-1}\).

7、\(3\) 提示    利用立方差公式.

8、\(7\) 提示    \(f(x)=\sqrt[3]{x+1}-\sqrt[3]{x}\).

9、\(4\) 提示    利用平方差公式.

10、\(0\) 提示    原式即\[\left(\dfrac{x}{y+z}+\dfrac{y}{z+x}+\dfrac{z}{x+y}\right)(x+y+z)-\cdots,\]而多出来的部分恰好为\(x+y+z\).

11、\(5\) 提示    三式相乘可整理得\[abc=\sum_{cyc}{a\left(\dfrac{by}z+\dfrac{cz}y\right)^2}-4abc.\]

12、\(1\) 提示    消元即可.

13、\(1\) 提示    \(a-b=\dfrac{c-b}{bc}\),轮换相乘即得.

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