共50条信息
\((\)Ⅰ\()\)证明:若\(a\),\(b\),\(c∈R^{+}\),则\(a+\dfrac{1}{b}\),\(b+\dfrac{1}{c}\),\(c+\dfrac{1}{a}\),至少有一个不小于\(2\);
\((\)Ⅱ\()\)设\(a\),\(b\),\(c\),\(d\)均为正数,且\(a+b=c+d\),若\(ab > cd\),证明:\(|a\)一\(b| < |c-d|\).
用反证法证明:在\(\Delta ABC\)中,若\(\angle C\)是直角,则\(\angle B\)一定是锐角.
用反证法证明:如果\(x > \dfrac{1}{2}\)那么\({{x}^{2}}+2x-1\ne 0\).
\((1)\)用综合法证明:\(a+b+c⩾ \sqrt{ab}+ \sqrt{bc}+ \sqrt{ca}(a,b,c∈{R}^{+}) \)
\((2)\)用反证法证明:若\(a{,}b{,}c\)均为实数,且\(a{=}x^{2}{-}2y{+}\dfrac{\pi}{2}{,}b{=}y^{2}{-}2z{+}\dfrac{\pi}{3}{,}c{=}z^{2}{-}2x{+}\dfrac{\pi}{6}\),求证:\(a{,}b{,}c\)中至少有一个大于\(0\).
已知\(a\)、\(b\)、\(c\)是互不相等的非零实数\(.\)用反证法证明三个方程\(ax^{2}+2bx+c=0\),\(bx^{2}+2cx+a=0\),\(cx^{2}+2ax+b=0\)至少有一个方程有两个相异实根.
\((1)\)证明不等式:\(\dfrac{x}{\sqrt{y}}+\dfrac{y}{\sqrt{x}}\geqslant \sqrt{x}+\sqrt{y}\)\((\)其中\(x\),\(y\)皆为正数\()\)
\((2)\)已知\(a > 0 \),\(b > 0\),\(a+b > 2\),求证:\(\dfrac{1+b}{a}, \dfrac{1+a}{b} \) 至少有一个小于\(2\).
设\(a,b,c\in (-\infty ,0)\),则\(a+\dfrac{1}{b},b+\dfrac{1}{c},c+\dfrac{1}{a}\)
如果无穷数列\(\{{{a}_{n}}\}\)满足下列条件:\(①\dfrac{{{a}_{n}}+{{a}_{n+2}}}{2}\leqslant {{a}_{n+1}}\);\(②\)存在实数\(M\),使得\({{a}_{n}}\leqslant M\),其中\(n\in {{N}^{*}}\),那么我们称数列\(\{{{a}_{n}}\}\)为\(\Omega \)数列.
\((1)\)设数列\(\{{{b}_{n}}\}\)的通项为\({{b}_{n}}=5n-{{2}^{n}}\),且是\(\Omega \)数列,求\(M\)的取值范围;
\((2)\)设\(\{{{c}_{n}}\}\)是各项为正数的等比数列,\({{S}_{n}}\)是其前\(n\)项和,\({{c}_{3}}=\dfrac{1}{4},{{S}_{3}}=\dfrac{7}{4}\),证明:数列\(\{{{S}_{n}}\}\)是\(\Omega \)数列;
\((3)\)设数列\(\{{{d}_{n}}\}\)是各项均为正整数的\(\Omega \)数列,求证:\({{d}_{n}}\leqslant {{d}_{n+1}}\).
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