`1)`
`\sqrt{12}+\sqrt{27}`
`=\sqrt{4.3}+\sqrt{9.3}`
`=2\sqrt{3}+3\sqrt{3}`
`=5\sqrt{3}`
`2)`
`3\sqrt{2}+5\sqrt{8}-2\sqrt{50}`
`=3\sqrt{2}+5\sqrt{4.2}-2\sqrt{25.2}`
`=3\sqrt{2}+5.2\sqrt{2}-2.5\sqrt{2}`
`=3\sqrt{2}+10\sqrt{2}-10\sqrt{2}`
`=3\sqrt{2}`
`3)`
`2\sqrt{45}+\sqrt{80}-\sqrt{245}`
`=2\sqrt{9.5}+\sqrt{16.5}-\sqrt{49.5}`
`=2.3\sqrt{5}+4\sqrt{5}-7\sqrt{5}`
`=6\sqrt{5}+4\sqrt{5}-7\sqrt{5}`
`=3\sqrt{5}`
`4)`
`3\sqrt{12}-\sqrt{27}+\sqrt{108}`
`=3\sqrt{4.3}-\sqrt{9.3}+\sqrt{36.3}`
`=3.2\sqrt{3}-3\sqrt{3}+6\sqrt{3}`
`=6\sqrt{3}-3\sqrt{3}+6\sqrt{3}`
`=9\sqrt{3}`
`5)`
`\sqrt{3/4}+\sqrt{1/3}+\sqrt{1/12}`
`=\sqrt{1/4 .3}+\sqrt{1/9 .3}+\sqrt{1/36 .3}`
`=1/2 .\sqrt{3}+1/3 .\sqrt{3}+1/6 .\sqrt{3}`
`=(1/2+1/3+1/6).\sqrt{3}`
`=\sqrt{3}`
`6)`
`\sqrt{0,4}+\sqrt{2,5}`
`=\sqrt{4/10}+\sqrt{25/10}`
`=\sqrt{4 .1/10}+\sqrt{25 . 1/10}`
`=2\sqrt{1/10}+5\sqrt{1/10}`
`=7 .\sqrt{1/10}`
`=7/\sqrt{10}`
`7)`
`(\sqrt{2}+\sqrt{72}-\sqrt{18}).\sqrt{2}`
`=(\sqrt{2}+\sqrt{36.2}-\sqrt{9.2}).\sqrt{2}`
`=(\sqrt{2}+6\sqrt{2}-3\sqrt{2}).\sqrt{2}`
`=4\sqrt{2}.\sqrt{2}`
`=4.2`
`=8`
`8)`
`(3\sqrt{5}+\sqrt{2}).(3\sqrt{5}-\sqrt{2})`
`=(3\sqrt{5})^2-(\sqrt{2})^2`
`=45-2`
`=43`
