3:
1: \(x-7=\left(\sqrt{x}-\sqrt{7}\right)\left(\sqrt{x}+\sqrt{7}\right)\)
2: \(2+x=2-\left(-x\right)=\left(\sqrt{2}-\sqrt{-x}\right)\left(\sqrt{2}+\sqrt{-x}\right)\)
3: \(x-6\sqrt{x}+9=\left(\sqrt{x}-3\right)^2\)
4: \(=\left(\sqrt{x}-\sqrt{y}\right)\left(\sqrt{x}+\sqrt{y}\right)-\left(\sqrt{x}+\sqrt{y}\right)\)
=(căn x+căn y)(căn x-căn y-1)
5: \(x\sqrt{y}-y\sqrt{x}=\sqrt{xy}\left(\sqrt{x}-\sqrt{y}\right)\)
6: \(x\sqrt{x}+1=\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)\)
7: \(x-5\sqrt{x}+6=\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)\)
8: \(x-\sqrt{x}-2=\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)\)
9: \(=2^3-\left(\sqrt{x}\right)^3=\left(2-\sqrt{x}\right)\left(4+2\sqrt{x}+x\right)\)
2:
1: 5căn 11>5*căn 9=15
=>-5căn 11<-15
2: 2căn 2<3
=>7+2*căn 2<7+3
=>7+2*căn 2<10
3: 2căn 3=căn 12
3*căn 2=căn 18
=>2*căn 3<3*căn 2
=>\(\sqrt{2\sqrt{3}}< \sqrt{3\sqrt{2}}\)