题霸题霸学习平台
← 返回公开题库
八年级数学填空题一般
题目
阅读材料:像(5+2)×(52)=1,aa=a(a0)(\sqrt{5}+2)×(\sqrt{5}-2)=1,\sqrt{a}•\sqrt{a}=a(a≥0)\ldots \ldots这种两个含二次根式的代数式相乘,积不含二次根式,我们称这两个代数式互为有理化因式.在进行二次根式运算时,利用有理化因式可以化去分母中的根号.数学课上,老师出了一道题"已知a=121a=\frac{1}{\sqrt{2}-1},求3a26a13a^{2}-6a-1的值".
聪明的小明同学根据上述材料,做了这样的解答:
因为a=121=2+1(21)×(2+1)=2+1a=\frac{1}{\sqrt{2}-1}=\frac{\sqrt{2}+1}{(\sqrt{2}-1)×(\sqrt{2}+1)}=\sqrt{2}+1,
所以a1=2a-1=\sqrt{2},
所以(a1)2=2\left(a-1\right)^{2}=2,所以a22a+1=2a^{2}-2a+1=2,
所以a22a=1a^{2}-2a=1,所以3a26a=33a^{2}-6a=3,所以3a26a1=23a^{2}-6a-1=2.
请你根据上述材料和小明的解答过程,解决如下问题:
(1)32(1)\sqrt{3}-\sqrt{2}的有理化因式是______.132=\frac{1}{\sqrt{3}-\sqrt{2}}=______;
(2)(2)比较大小:20242023\sqrt{2024}-\sqrt{2023}______20232022(\sqrt{2023}-\sqrt{2022}(>\gt,<\lt,==,\geqslant\leqslant中的一种);
(3)(3)计算:(12+1+13+2+14+3++12022+2021)(2022+1)(\frac{1}{\sqrt{2}+1}+\frac{1}{\sqrt{3}+\sqrt{2}}+\frac{1}{\sqrt{4}+\sqrt{3}}+⋯+\frac{1}{\sqrt{2022}+\sqrt{2021}})(\sqrt{2022}+1)
(4)(4)a=237a=\frac{2}{3-\sqrt{7}},求2a2+12a+3-2a^{2}+12a+3的值.
知识点:分式的基本性质、约分、分式的加减法章节:第18章 分式 / 18.1 分式及其基本性质 / 18.1.2 分式的基本性质

答案与解析

答案

(1)由题知,32\sqrt{3}-\sqrt{2}的有理化因式是3+2\sqrt{3}+\sqrt{2}
132=3+2(32)(3+2)=3+2\therefore \frac{1}{\sqrt{3}-\sqrt{2}}=\frac{\sqrt{3}+\sqrt{2}}{(\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2})}=\sqrt{3}+\sqrt{2}.
故答案为:3+2\sqrt{3}+\sqrt{2}3+2\sqrt{3}+\sqrt{2}
(2)120242023=2024+2023(2)\because \frac{1}{\sqrt{2024}-\sqrt{2023}}=\sqrt{2024}+\sqrt{2023}120232022=2023+2022\frac{1}{\sqrt{2023}-\sqrt{2022}}=\sqrt{2023}+\sqrt{2022}
显然2024+20232023+2022\sqrt{2024}+\sqrt{2023}>\sqrt{2023}+\sqrt{2022},即120242023120232022\frac{1}{\sqrt{2024}-\sqrt{2023}}>\frac{1}{\sqrt{2023}-\sqrt{2022}}
20242023\because \sqrt{2024}-\sqrt{2023}20232022\sqrt{2023}-\sqrt{2022}都是大于00的数,
2024202320232022\therefore \sqrt{2024}-\sqrt{2023}<\sqrt{2023}-\sqrt{2022}
故答案为:<\lt
(3)(12+1+13+2+14+3++12022+2021)(2022+1)(3)(\frac{1}{\sqrt{2}+1}+\frac{1}{\sqrt{3}+\sqrt{2}}+\frac{1}{\sqrt{4}+\sqrt{3}}+⋯+\frac{1}{\sqrt{2022}+\sqrt{2021}})(\sqrt{2022}+1)
=(21+32+43+•••+20222021)×(2022+1)=(\sqrt{2}-1+\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+•••+\sqrt{2022}-\sqrt{2021})×(\sqrt{2022}+1)
=(20221)×(2022+1)=(\sqrt{2022}-1)×(\sqrt{2022}+1)
=20221=2022-1
=2021=2021
(4)a=237=2×(3+7)(37)×(3+7)=3+7(4)\because a=\frac{2}{3-\sqrt{7}}=\frac{2×(3+\sqrt{7})}{(3-\sqrt{7})×(3+\sqrt{7})}=3+\sqrt{7}
a3=7\therefore a-3=\sqrt{7}
(a3)2=7\therefore \left(a-3\right)^{2}=7
a26a+9=7\therefore a^{2}-6a+9=7
a26a=2\therefore a^{2}-6a=-2
2a2+12a=4\therefore -2a^{2}+12a=4
2a2+12a+3=7\therefore -2a^{2}+12a+3=7.

解析

(1)由题知,32\sqrt{3}-\sqrt{2}的有理化因式是3+2\sqrt{3}+\sqrt{2}
132=3+2(32)(3+2)=3+2\therefore \frac{1}{\sqrt{3}-\sqrt{2}}=\frac{\sqrt{3}+\sqrt{2}}{(\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2})}=\sqrt{3}+\sqrt{2}.
故答案为:3+2\sqrt{3}+\sqrt{2}3+2\sqrt{3}+\sqrt{2}
(2)120242023=2024+2023(2)\because \frac{1}{\sqrt{2024}-\sqrt{2023}}=\sqrt{2024}+\sqrt{2023}120232022=2023+2022\frac{1}{\sqrt{2023}-\sqrt{2022}}=\sqrt{2023}+\sqrt{2022}
显然2024+20232023+2022\sqrt{2024}+\sqrt{2023}>\sqrt{2023}+\sqrt{2022},即120242023120232022\frac{1}{\sqrt{2024}-\sqrt{2023}}>\frac{1}{\sqrt{2023}-\sqrt{2022}}
20242023\because \sqrt{2024}-\sqrt{2023}20232022\sqrt{2023}-\sqrt{2022}都是大于00的数,
2024202320232022\therefore \sqrt{2024}-\sqrt{2023}<\sqrt{2023}-\sqrt{2022}
故答案为:<\lt
(3)(12+1+13+2+14+3++12022+2021)(2022+1)(3)(\frac{1}{\sqrt{2}+1}+\frac{1}{\sqrt{3}+\sqrt{2}}+\frac{1}{\sqrt{4}+\sqrt{3}}+⋯+\frac{1}{\sqrt{2022}+\sqrt{2021}})(\sqrt{2022}+1)
=(21+32+43+•••+20222021)×(2022+1)=(\sqrt{2}-1+\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+•••+\sqrt{2022}-\sqrt{2021})×(\sqrt{2022}+1)
=(20221)×(2022+1)=(\sqrt{2022}-1)×(\sqrt{2022}+1)
=20221=2022-1
=2021=2021
(4)a=237=2×(3+7)(37)×(3+7)=3+7(4)\because a=\frac{2}{3-\sqrt{7}}=\frac{2×(3+\sqrt{7})}{(3-\sqrt{7})×(3+\sqrt{7})}=3+\sqrt{7}
a3=7\therefore a-3=\sqrt{7}
(a3)2=7\therefore \left(a-3\right)^{2}=7
a26a+9=7\therefore a^{2}-6a+9=7
a26a=2\therefore a^{2}-6a=-2
2a2+12a=4\therefore -2a^{2}+12a=4
2a2+12a+3=7\therefore -2a^{2}+12a+3=7.

AI 自由组卷

围绕这道题再组一份练习 →

完整试卷

浏览同年级试卷结构 →