Đáp án:

`1)\sqrt{45}+\sqrt{20}-\sqrt{180}`

`=3\sqrt{5}+2\sqrt{5}-6\sqrt{5}`

`=-\sqrt{5}`

`2)5\sqrt{3}+\sqrt{12}-\sqrt{27}`

`=5\sqrt{3}+2\sqrt{3}-3\sqrt{3}2`

`=4\sqrt{3}`

`3)\sqrt{12}+5\sqrt{3}-\sqrt{48}`

`=2\sqrt{3}+5\sqrt{3}-4\sqrt{3}`

`=3\sqrt{3}`

`4)\sqrt{12}+\sqrt{75}-\sqrt{27}`

`=2\sqrt{3}+5\sqrt{3}-3\sqrt{3}`

`=4\sqrt{3}`

`5)3\sqrt{5}-\sqrt{20}-7\sqrt{5}`

`=3\sqrt{5}-2\sqrt{5}-7\sqrt{5}`

`=-6\sqrt{5}`

`6)\sqrt{32}-2\sqrt{18}+4\sqrt{50}`

`=4\sqrt{2}-6\sqrt{2}+20\sqrt{2}`

`=18\sqrt{2}`

`7)5\sqrt{18}-2\sqrt{50}+\sqrt{72}`

`=15\sqrt{2}-10\sqrt{2}+6\sqrt{2}`

`=11\sqrt{2}`

`8)2\sqrt{32}-3\sqrt{98}-6\sqrt{200}`

`=8\sqrt{2}-21\sqrt{2}-60\sqrt{2}`

`=-73\sqrt{2}`

`9)3\sqrt{2}+\sqrt{8}-\sqrt{50}`

`=3\sqrt{2}+2\sqrt{2}-5\sqrt{2}`

`=0`

`10)5\sqrt{5}+\sqrt{20}-3\sqrt{45}`

`=5\sqrt{5}+2\sqrt{5}-9\sqrt{5}`

`=-2\sqrt{5}`

`11)2\sqrt{32}+4\sqrt{8}-5\sqrt{18}`

`=8\sqrt{2}+8\sqrt{2}-15\sqrt{2}`

`=\sqrt{2}`

`12)2\sqrt{8}-7\sqrt{2}+\sqrt{162}`

`=4\sqrt{2}-7\sqrt{2}+9\sqrt{2}`

`=6\sqrt{2}`

`13)2\sqrt{48}-3\sqrt{75}+\sqrt{27}`

`=8\sqrt{3}-15\sqrt{3}+3\sqrt{3}`

`=-4\sqrt{3}`

`14)2\sqrt{8}+3\sqrt{18}-\sqrt{50}`

`=4\sqrt{2}+9\sqrt{2}-5\sqrt{2}`

`=8\sqrt{2}`

`15)5\sqrt{27}-3\sqrt{3}+2\sqrt{48}`

`=15\sqrt{3}-3\sqrt{3}+8\sqrt{3}`

`=26\sqrt{3}`

`@Zenitsu`

Giải thích các bước giải: