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a) P = \(\left(\frac{3\sqrt{a}}{a+\sqrt{a}+b}-\frac{3a}{a\sqrt{a}-b\sqrt{b}}+\frac{1}{\sqrt{a}-\sqrt{b}}\right):\frac{\left(a-1\right).\left(\sqrt{a}-\sqrt{b}\right)}{\left(2.a+2.\sqrt{ab}+2.b\right)}\)
= \(\left(\frac{3\sqrt{a}.\left(\sqrt{a}-\sqrt{b}\right)-3.a+a+\sqrt{ab}+b}{\left(\sqrt{a}-\sqrt{b}\right).\left(a+\sqrt{ab}+b\right)}\right).\frac{2.\left(a+\sqrt{ab}+b\right)}{\left(a-1\right).\left(\sqrt{a}-\sqrt{b}\right)}\)
= \(\frac{a-2.\sqrt{ab}+b}{\sqrt{a}-\sqrt{b}}.\frac{2}{\left(a-1\right).\left(\sqrt{a}-\sqrt{b}\right)}\)
= \(\frac{2}{a-1}\)
b) P nguyên <=> \(\frac{2}{a-1}\)nguyên => 2 \(⋮\)a - 1
=> ( a- 1 ) = { \(\pm\)1 ; \(\pm\) 2} => a = { -1 ; 0 ; 2 ;3 }
Ta có : \(P=\frac{a^3-a-2b-\frac{b^2}{a}}{\left(\frac{1}{\sqrt{a}}-\sqrt{\frac{1}{a}+\frac{b}{a^2}}\right)\left(\sqrt{a}+\sqrt{a+b}\right)}:\left(\frac{a^3+a^2+ab+a^2b}{a^2-b^2}+\frac{b}{a-b}\right)\)
=> \(P=\frac{\frac{a^4}{a}-\frac{a^2}{a}-\frac{2ab}{a}-\frac{b^2}{a}}{\left(\frac{1}{\sqrt{a}}-\sqrt{\frac{1}{a}+\frac{b}{a^2}}\right)\left(\sqrt{a}+\sqrt{a+b}\right)}:\left(\frac{a^2\left(a+1\right)+ab\left(a+1\right)}{\left(a-b\right)\left(a+b\right)}+\frac{b}{a-b}\right)\)
=> \(P=\frac{\frac{a^4-a^2-2ab-b^2}{a}}{\frac{\sqrt{a}}{\sqrt{a}}-\sqrt{a\left(\frac{1}{a}+\frac{b}{a^2}\right)}+\sqrt{\frac{a+b}{a}}-\sqrt{\left(a+b\right)\left(\frac{1}{a}+\frac{b}{a^2}\right)}}:\left(\frac{a\left(a+b\right)\left(a+1\right)}{\left(a-b\right)\left(a+b\right)}+\frac{b}{a-b}\right)\)
=> \(P=\frac{\frac{a^4-\left(a^2+2ab+b^2\right)}{a}}{1-\sqrt{\frac{a}{a}+\frac{ab}{a^2}}+\sqrt{\frac{a+b}{a}}-\sqrt{\frac{a}{a}+\frac{b}{a}+\frac{ab}{a^2}+\frac{b^2}{a^2}}}:\left(\frac{a\left(a+1\right)+b}{a-b}\right)\)
=> \(P=\frac{\frac{a^4-\left(a^2+2ab+b^2\right)}{a}}{1-\sqrt{1+\frac{b}{a}}+\sqrt{\frac{a+b}{a}}-\sqrt{1+\frac{2b}{a}+\frac{b^2}{a^2}}}:\left(\frac{a\left(a+1\right)+b}{a-b}\right)\)
=> \(P=\frac{\frac{a^4-\left(a+b\right)^2}{a}\left(a-b\right)}{\left(1-\sqrt{1+\frac{b}{a}}+\sqrt{\frac{a+b}{a}}-\left(\frac{b}{a}+1\right)\right)\left(a\left(a+1\right)+b\right)}\)
=> \(P=\frac{\frac{\left(a^2-a-b\right)\left(a^2+a+b\right)\left(a-b\right)}{a}}{\left(1-\frac{b}{a}-1\right)\left(a\left(a+1\right)+b\right)}\)\(=\frac{\frac{\left(a^2-a-b\right)\left(a^2+a+b\right)\left(a-b\right)}{a}}{\frac{b\left(a^2+a+b\right)}{a}}\)\(=\frac{\left(a^2-a-b\right)\left(a^2+a+b\right)\left(a-b\right)}{b\left(a^2+a+b\right)}\)
=> \(P=\frac{\left(a^2-a-b\right)\left(a-b\right)}{b}\)
- Thay a = 23, b = 22 vào biểu thức trên ta được :
\(P=\frac{\left(23^2-23-22\right)\left(23-22\right)}{22}=22\)
1) \(VT=\frac{\sqrt{a}+\sqrt{b}}{2\left(\sqrt{a}-\sqrt{b}\right)}-\frac{\sqrt{a}-\sqrt{b}}{2\left(\sqrt{a}+\sqrt{b}\right)}+\frac{2b}{\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}\)
\(=\frac{\left(\sqrt{a}+\sqrt{b}\right)^2-\left(\sqrt{a}-\sqrt{b}\right)^2+4b}{2\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}\)\(=\frac{a+2\sqrt{ab}+b-a+2\sqrt{ab}-b+4b}{2\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}\)
\(=\frac{4\sqrt{ab}+4b}{2\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}\)
\(=\frac{4\sqrt{b}\left(\sqrt{a}+\sqrt{b}\right)}{2\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}=\frac{2\sqrt{b}}{\sqrt{a}-\sqrt{b}}=VP\)(ĐPCM)
2) \(VT=\text{[}\frac{\left(\sqrt{a}+\sqrt{b}\right)\left(a+b-\sqrt{ab}\right)}{\left(\sqrt{a}+\sqrt{b}\right)}-\sqrt{ab}\text{]}.\frac{\left(\sqrt{a}+\sqrt{b}\right)^2}{\left(a-b\right)^2}\)
\(=\frac{\left(a+b-\sqrt{ab}-\sqrt{ab}\right)\left(\sqrt{a}+\sqrt{b}\right)^2}{\left(a-b\right)^2}\)\(=\frac{\left(\sqrt{a}-\sqrt{b}\right)^2\left(\sqrt{a}+\sqrt{b}\right)^2}{\left(a-b\right)^2}=\frac{\left(a-b\right)^2}{\left(a-b\right)^2}=1=VP\)(ĐPCM)
4) \(VT=\left(1+\frac{a+\sqrt{a}}{\sqrt{a}+1}\right)\left(1-\frac{a-\sqrt{a}}{\sqrt{a}-1}\right)\)\(=\left(1+\frac{\sqrt{a}\left(\sqrt{a}+1\right)}{\sqrt{a}+1}\right)\left(1-\frac{\sqrt{a}\left(\sqrt{a}-1\right)}{\sqrt{a}-1}\right)\)
\(=\left(1+\sqrt{a}\right)\left(1-\sqrt{a}\right)=1-a=VP\)(ĐPCM)
