c)
`(2\sqrt{15}-2\sqrt{10}+\sqrt{6}-3)/(2\sqrt{5}-2\sqrt{10}-\sqrt{3}+\sqrt{6})`
`⇔[2\sqrt{5}(\sqrt{3}-\sqrt{2})-\sqrt{3}(\sqrt{3}-\sqrt{2})]/[2\sqrt{5}(1-\sqrt{2})-\sqrt{3}(1-\sqrt{2})`
`⇔[(2\sqrt{5}-\sqrt{3})(\sqrt{3}-\sqrt{2})]/[(2\sqrt{5}-\sqrt{3})(1-\sqrt{2})]`
`⇔(\sqrt{3}-\sqrt{2})/(1-\sqrt{2})`
f)
`(\sqrt{a}+a\sqrt{b}-\sqrt{b}-b\sqrt{a})/(ab-1)`
`⇔[(\sqrt{a})(1+\sqrt{ab})-(\sqrt{b})(1+\sqrt{ab})]/[(\sqrt{ab}-1)(\sqrt{ab}+1)]`
`⇔[(\sqrt{a}-\sqrt{b})(1+\sqrt{ab})]/[(\sqrt{ab}-1)(\sqrt{ab}+1)]`
`⇔(\sqrt{a}-\sqrt{b})/(\sqrt{ab}-1)`
