`a)VP=\sqrt{8-2\sqrt{15}}`
`=\sqrt{5-2.\sqrt{3.5}+3}`
`=\sqrt{(\sqrt{5})^2-2.\sqrt{5}.\sqrt{3}+(\sqrt{3})^2}`
`=\sqrt{(\sqrt{5}-\sqrt{3})^2}`
`=|\sqrt{5}-\sqrt{3}|`
`=\sqrt{5}-\sqrt{3}`
`=VT`
`⇒đpcm`
`b)VT=(3+\sqrt{5})(3-\sqrt{5})-(2+\sqrt{3})(2-\sqrt{3})`
`=3^2-(\sqrt{5})^2-[2^2-(\sqrt{3})^2]`
`=9-5-(4-3)`
`=4-1`
`=3`
`=VP`
`⇒đpcm`