`a,\sqrt{10+2\sqrt{6}-2\sqrt{10}-2\sqrt{15}}`
`=\sqrt{2+3+5+2.\sqrt{2}.\sqrt{3}-2.\sqrt{5}.\sqrt{2}-2.\sqrt{3}.\sqrt{5}}`
`=\sqrt{(\sqrt{2}+\sqrt{3}-\sqrt{5})^2}`
`=\sqrt{2}+\sqrt{3}-\sqrt{5}`
`b,\sqrt{7-2\sqrt{10}}-\sqrt{7+2\sqrt{10}}`
`=\sqrt{5-2.\sqrt{2}.\sqrt{5}+2}-\sqrt{5+2./sqrt{2}.\sqrt{5}+2}`
`=\sqrt{(\sqrt{5}-\sqrt{2})^2}+\sqrt{(\sqrt{5}+\sqrt{2})^2}`
`=\sqrt{5}-\sqrt{2}+\sqrt{5}+\sqrt{2}`
`=2\sqrt{5}`
`c,\sqrt{5-2\sqrt{6}}-\sqrt{5+2\sqrt{6}}`
`=\sqrt{3-2.\sqrt{2}.\sqrt{3}+2}-\sqrt{3+2.\sqrt{2}.\sqrt{3}+2}`
`=\sqrt{(\sqrt{3}-\sqrt{2})^2}-\sqrt{(\sqrt{3}+\sqrt{2})^2}`
`=\sqrt{3}-\sqrt{2}-\sqrt{3}-\sqrt{2}`
`=-2\sqrt{2}`
