`a,2\sqrt{32}+3\sqrt{72}-7\sqrt{50}+\sqrt{2}`
`=8\sqrt{2}+18\sqrt{2}-35\sqrt{2}+\sqrt{2}`
`=-8\sqrt{2}`
`b,\sqrt{(\sqrt{5}-\sqrt{7})^2}+4\sqrt{20}+\sqrt{28}`
`=|\sqrt{5}-\sqrt{7}|+8\sqrt{5}+2\sqrt{7}`
`=\sqrt{7}-\sqrt{5}+8\sqrt{5}+2\sqrt{7}`
`=3\sqrt{7}+7\sqrt{5}`
`c,2+3\sqrt{2}-2\sqrt{32}-\sqrt{6+4\sqrt{2}}`
`=2+3\sqrt{2}-8\sqrt{2}-\sqrt{6+2\sqrt{8}}`
`=2-5\sqrt{2}-\sqrt{4+2\sqrt{8}+2}`
`=2-5\sqrt{2}-\sqrt{(\sqrt{4}+\sqrt{2})^2}`
`=2-5\sqrt{2}-\sqrt{(2+\sqrt{2})^2}`
`=2-5\sqrt{2}-|2+\sqrt{2}|`
`=2-5\sqrt{2}-(2+\sqrt{2})`
`=2-5\sqrt{2}-2-\sqrt{2}`
`=-6\sqrt{2}`
