Đáp án:+Giải thích các bước giải:
19) `2/(\sqrt3-\sqrt5)-(3-2\sqrt3)/(2-\sqrt3)`
`= (2(\sqrt3+\sqrt5))/((\sqrt3-\sqrt5)(\sqrt3+\sqrt5))-((3-2\sqrt3)(2+\sqrt3))/((2-\sqrt3)(2+\sqrt3)`
`=(2(\sqrt3+\sqrt5))/(-2)- (6+3\sqrt3-4\sqrt3-6)/1`
`=-(\sqrt3+\sqrt5) - (-\sqrt3)`
`=-\sqrt3-\sqrt5+\sqrt3=-\sqrt5`
20) `(3\sqrt2-2\sqrt3)/(\sqrt3-\sqrt2)-5/(1+\sqrt6)`
`=(\sqrt2.\sqrt3.(\sqrt3-\sqrt2))/(\sqrt3-\sqrt2)-(5(1-\sqrt6))/((1+\sqrt6)(1-\sqrt6))`
`=\sqrt2.\sqrt3-(5(1-\sqrt6))/-5`
`=\sqrt6+1-\sqrt6=1`
21) `(\sqrt15+\sqrt10)/(\sqrt3+\sqrt2)-1/(\sqrt5-2)`
`=(\sqrt5(\sqrt3+\sqrt2))/(\sqrt3+\sqrt2)-(\sqrt5+2)/((\sqrt5-2)(\sqrt5+2))`
`=\sqrt5-(\sqrt5+2)/1=-2`
22) `(6\sqrt2-4)/(\sqrt2-\sqrt3)-(3\sqrt2-6)/(1-\sqrt2)`
`= ((6\sqrt2-4)(\sqrt2+\sqrt3))/((\sqrt2-\sqrt3)(\sqrt2+\sqrt3))-(3\sqrt2(1-\sqrt2))/(1-\sqrt2)`
`=(12+6\sqrt6-4\sqrt2-4\sqrt3)/-1-3\sqrt2`
`=-12-6\sqrt6+4\sqrt2+4\sqrt3-3\sqrt2`
`=-12-6\sqrt6+\sqrt2+4\sqrt3`
