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a: \(=3\sqrt{3}-2\sqrt{3}+4\sqrt{3}-5\sqrt{3}=2\sqrt{3}\)
\(a, x^3+5x^2-9x-45=0\\ \Leftrightarrow x^2\left(x+5\right)-9\left(x+5\right)=0\\ \Leftrightarrow\left(x-3\right)\left(x+3\right)\left(x+5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\left(x\ne-5\right)\\ \text{Với }x=3\Leftrightarrow A=\dfrac{9-9}{3\left(3+5\right)}=0\\ \text{Với }x=-3\Leftrightarrow A=\dfrac{9-9}{3\left(-3+5\right)}=0\\ \text{Vậy }A=0\\ b,B=\dfrac{x^2-3x+2x^2+6x-3x^2-9}{\left(x-3\right)\left(x+3\right)}\\ B=\dfrac{3x-9}{\left(x-3\right)\left(x+3\right)}=\dfrac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}=\dfrac{3}{x+3}\)
b: \(B=\dfrac{x^2-3x+2x^2+6x-3x^2-9}{x^2-9}=\dfrac{3x-9}{\left(x-3\right)\left(x+3\right)}=\dfrac{3}{x+3}\)
b: \(B=\dfrac{x^2-3x+2x^2+6x-3x^2-9}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{3x-9}{\left(x-3\right)\left(x+3\right)}=\dfrac{3}{x+3}\)
a) Ta có: \(\dfrac{x+\sqrt{5}}{x^2+2x\sqrt{5}+5}\)
\(=\dfrac{x+\sqrt{5}}{\left(x+\sqrt{5}\right)^2}=\dfrac{1}{x+\sqrt{5}}\)
b) Ta có: \(B=\dfrac{a-2\sqrt{a}-3}{a-9}\)
\(=\dfrac{\left(\sqrt{a}-3\right)\left(\sqrt{a}+1\right)}{\left(\sqrt{a}-3\right)\left(\sqrt{a}+3\right)}\)
\(=\dfrac{\sqrt{a}+1}{\sqrt{a}+3}\)
c) Ta có: \(C=\sqrt{x-1-2\sqrt{x-2}}\)
\(=\sqrt{x-2-2\cdot\sqrt{x-2}\cdot1+1}\)
\(=\sqrt{\left(\sqrt{x-2}-1\right)^2}\)
\(=\left|\sqrt{x-2}-1\right|\)
`a)A=(x+sqrt5)(x^2+2xsqrt5+5)`
`=(x+sqrt5)/(x+sqrt5)^2=1/(x+sqrt5)`
`b)B=(a-2sqrta-3)/(a-9)(a>=0,a ne 9)`
`=(a+sqrta-3sqrta-3)/(a-9)`
`=((sqrta+1)(sqrta-3))/((sqrta-3)(sqrta+3))`
`=(sqrta+1)/(sqrta+3)`
`c)C=sqrt{x-1-2sqrt{x-2}}(x>=2)`
`=sqrt{x-2-2sqrt{x-2}+1}`
`=sqrt{(sqrt{x-2}-1)^2}`
`=|sqrt(x-2)-1|`
a) Ta có: \(5\sqrt{a}-3\sqrt{25a^3}+2\sqrt{36ab^2}-2\sqrt{9a}\)
\(=5\sqrt{a}-15a\sqrt{a}+12b\sqrt{a}-6\sqrt{a}\)
\(=-\sqrt{a}-15a\sqrt{a}+12\sqrt{a}b\)
b) Ta có: \(\sqrt{64ab^3}-3\sqrt{12a^3b^3}+2ab\sqrt{9ab}-5b\sqrt{81a^3b}\)
\(=8b\sqrt{a}-6ab\sqrt{3ab}+6ab\sqrt{ab}-45a^2b\sqrt{ab}\)
a)\(5\sqrt{a}-3\sqrt{25a^3}+2\sqrt{36ab^2}-2\sqrt{9a}=5\sqrt{a}-15\left|a\right|\sqrt{a}+12\left|b\right|\sqrt{a}-6\sqrt{a}=-\sqrt{a}-15a\sqrt{a}+12b\sqrt{a}\)
b)\(\sqrt{64ab^3}-3\sqrt{12a^3b^3}+2ab\sqrt{9ab}-5b\sqrt{81a^3b}\)
\(=8\left|b\right|\sqrt{ab}-6\left|ab\right|\sqrt{3ab}+6ab\sqrt{ab}-45b\left|a\right|\sqrt{ab}\)
\(=8b\sqrt{ab}-6ab\sqrt{3ab}+6ab\sqrt{ab}-45ab\sqrt{ab}\)
\(=8b\sqrt{ab}-6ab\sqrt{3ab}-39ab\sqrt{ab}\)
a: Thay x=16 vào A, ta được:
\(A=\dfrac{2\cdot4}{4+3}=\dfrac{8}{7}\)
= 5√a - 4b.5a√a + 5a.4b√a - 2.3√a
= 5√a - 20ab√a + 20ab√a - 6√a = -√a