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Đặt: \(A=\sqrt{3+\sqrt{8}}\)
=> \(\sqrt{2}A=\sqrt{6+2\sqrt{8}}=\sqrt{\left(2+\sqrt{2}\right)^2}=2+\sqrt{2}=\sqrt{2}\left(\sqrt{2+1}\right)\)
=> \(A=\sqrt{2}+1\)
\(3+\sqrt{18}+\sqrt{3+\sqrt{8}}=3+3\sqrt{2}+\sqrt{2}+1\)
\(=3\left(\sqrt{2}+1\right)+\left(\sqrt{2}+1\right)=4.\left(\sqrt{2}+1\right)\)
Bài làm:
Ta có: \(-6x+5\sqrt{x}+1\)
\(=\left(-6x+6\sqrt{x}\right)-\left(\sqrt{x}-1\right)\)
\(=-6\sqrt{x}\left(\sqrt{x}-1\right)-\left(\sqrt{x}-1\right)\)
\(=\left(-6\sqrt{x}-1\right)\left(\sqrt{x}-1\right)\)
\(=\left(6\sqrt{x}+1\right)\left(1-\sqrt{x}\right)\)
\(\sqrt{x^3}-1=\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right).\)
A)=a+\(2\sqrt{a}+2\sqrt{a}\)+4
=\(\sqrt{a}\left(\sqrt{a}+2\right)+2\left(\sqrt{a}+2\right)=\left(\sqrt{a}+2\right)^2\)
b)= \(\left(a-\sqrt{7}\right)\left(a+\sqrt{7}\right)\)
c) \(\sqrt{a}\left(\sqrt{b}-4\right)+3\cdot\left(\sqrt{b}-4\right)=\left(\sqrt{a}+3\right)\left(\sqrt{b}-4\right)\)
a ) \(x+\sqrt{x}=\left(\sqrt{x}\right)^2+\sqrt{x}=\sqrt{x}\left(\sqrt{x}+1\right)\)
b ) \(x-4\sqrt{x}+3=\left(\sqrt{x}\right)^2-2.\sqrt{x}.2+2^2-1=\left(\sqrt{x}-2\right)^2-1\)
\(=\left(\sqrt{x}-2\right)^2-1^2=\left(\sqrt{x}-2+1\right)\left(\sqrt{x}-2-1\right)=\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)\)
\(x+\sqrt{x}=\left(\sqrt{x}\right)^2+\sqrt{x}=\sqrt{x}.\left(\sqrt{x}+1\right)\)
\(x-4\sqrt{x}+3=\left[\left(\sqrt{x}\right)^2-2.\sqrt{x}.2+2^2\right]-1^2=\left(\sqrt{x}-2\right)^2-1^2\)
\(=\left(\sqrt{x}-2-1\right)\left(\sqrt{x}-2+1\right)\)
\(=\left(\sqrt{x}-3\right)\left(\sqrt{x}-1\right)\)
\(8-\frac{x\sqrt{x}}{3}\)
\(=8-\frac{\sqrt{x^3}}{3}\)
\(=8-\frac{\left(\sqrt{x}\right)^3}{3}\)
\(=8-\frac{\left(\sqrt{x}\right)^3}{\left(\sqrt[3]{3}\right)^3}\)
\(=2^3-\left(\frac{\sqrt{x}}{\sqrt[3]{3}}\right)^3\)
\(=\left(2-\frac{\sqrt{x}}{\sqrt[3]{3}}\right)\left(4+\frac{2\sqrt{x}}{\sqrt[3]{3}}+\frac{x}{\left(\sqrt[3]{3}\right)^2}\right)\)
alibaba nguyễn: Cái đó đúng là đa thức mà! Nhưng mà ko bt làm thôi à T_T!