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八年级数学解答题一般
题目

观察下列各式,通过分母有理化把不是最简二次根式的化成最简二次根式.

12+1=1×(21)(2+1)(21)=21(2)21=2121=21;\dfrac{1}{\sqrt{2}+1}=\dfrac{1\text{×}(\sqrt{2}-1)}{(\sqrt{2}+1)(\sqrt{2}-1)}=\dfrac{\sqrt{2}-1}{(\sqrt{2})^{2}-1}=\dfrac{\sqrt{2}-1}{2-1}=\sqrt{2}-1\text{;}
13+2=1×(32)(3+2)(32)=32(3)2(2)2=3232=32.\dfrac{1}{\sqrt{3}+\sqrt{2}}=\dfrac{1\text{×}(\sqrt{3}-\sqrt{2})}{(\sqrt{3}+\sqrt{2})(\sqrt{3}-\sqrt{2})}=\dfrac{\sqrt{3}-\sqrt{2}}{(\sqrt{3})^{2}-(\sqrt{2})^{2}}=\dfrac{\sqrt{3}-\sqrt{2}}{3-2}=\sqrt{3}-\sqrt{2}.

按照以上的过程,解答以下问题:

(1)(1)计算:14+3;\dfrac{1}{\sqrt{4}+\sqrt{3}}\text{;}
(2)(2)计算:(12+1+13+2+14+3+⋯+12021+2020)×(2021+1).(\dfrac{1}{\sqrt{2}+1}+\dfrac{1}{\sqrt{3}+\sqrt{2}}+\dfrac{1}{\sqrt{4}+\sqrt{3}}\text{+⋯+}\dfrac{1}{\sqrt{2021}+\sqrt{2020}})\text{×}(\sqrt{2021}+1).
知识点:平方差公式、二次根式分母有理化、二次根式的混合运算章节:第21章 二次根式 / 21.3 二次根式的加减

答案与解析

答案

解:(1)(1)原式=43(4+3)(43)=4343=43=\dfrac{\sqrt{4}-\sqrt{3}}{\left(\sqrt{4}+\sqrt{3}\right)\left(\sqrt{4}-\sqrt{3}\right)}=\dfrac{\sqrt{4}-\sqrt{3}}{4-3}=\sqrt{4}-\sqrt{3}
(2)(2)原式=(21+32+43++20212020)×(2021+1)=\left(\sqrt{2}-1+\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+…+\sqrt{2021}-\sqrt{2020}\right)×\left(\sqrt{2021}+1\right)
=(20211)(2021+1)=\left(\sqrt{2021}-1\right)\left(\sqrt{2021}+1\right)
=20211=2021-1
=2020.=2020.

解析

解:(1)(1)原式=43(4+3)(43)=4343=43=\dfrac{\sqrt{4}-\sqrt{3}}{\left(\sqrt{4}+\sqrt{3}\right)\left(\sqrt{4}-\sqrt{3}\right)}=\dfrac{\sqrt{4}-\sqrt{3}}{4-3}=\sqrt{4}-\sqrt{3}
(2)(2)原式=(21+32+43++20212020)×(2021+1)=\left(\sqrt{2}-1+\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+…+\sqrt{2021}-\sqrt{2020}\right)×\left(\sqrt{2021}+1\right)
=(20211)(2021+1)=\left(\sqrt{2021}-1\right)\left(\sqrt{2021}+1\right)
=20211=2021-1
=2020.=2020.

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