Đáp án:+Giải thích các bước giải:
a) `2\sqrt50-3\sqrt98+4\sqrt32-5\sqrt72`
`=2\sqrt(5^2. 2)-3\sqrt(7^2 .2)+4\sqrt(4^2 . 2)-5\sqrt(6^2. 2)`
`=2.5.\sqrt2-3.7.\sqrt2+4.4\sqrt2-5.6.\sqrt2`
`=10\sqrt2-21\sqrt2+16\sqrt2-30\sqrt2`
`=-25\sqrt2`
b) `\sqrt(4+2\sqrt3)-\sqrt(4-2\sqrt3)`
`=\sqrt((\sqrt3)^2+2.\sqrt3.1+1)-\sqrt((\sqrt3)^2-2.\sqrt3 .1+1)`
`=\sqrt((\sqrt3+1)^2)-\sqrt((\sqrt3-1)^2)`
`=|\sqrt3+1|-|\sqrt3-1|`
`=\sqrt3+1-(\sqrt3-1)`
`=\sqrt3+1-\sqrt3+1=2`
