a) `2\sqrt{48}-\sqrt{75}+\sqrt{300}`
`=8\sqrt{3}-5\sqrt{3}+10\sqrt{3}`
`=13\sqrt{3}`
b) `(\sqrt{2}-3)^2+\sqrt{72}-5`
`=2-6\sqrt{2}+9+6\sqrt{2}-5`
`=6`
c) `2/(3+\sqrt{7})-(2)/(3-\sqrt{7})`
`=(2(3-\sqrt{7}))/((3+\sqrt{7})(3-\sqrt{7}))-(2(3+\sqrt{7}))/((3-\sqrt{7})(3+\sqrt{7}))`
`=(2(3-\sqrt{7}))/(2)-(2(3+\sqrt{7}))/(2)`
`=3-\sqrt{7}-3-\sqrt{7}`
`=-2\sqrt{7}`
