`text{Đáp án:}`
`a) A = (\sqrt{3}-1)(\sqrt{3}+1)-(2-\sqrt{3})^2`
`A = 3-1-(4-4\sqrt{3}+3)`
`A = 2-4+4\sqrt{3}-3`
`A = 4\sqrt{3}-5`
`b) B = (\sqrt{5}-1)^2-(\sqrt{5}-2)^2`
`B = (\sqrt{5}-1-\sqrt{5}+2)(\sqrt{5}-1+\sqrt{5}-2)`
`B = 2\sqrt{5}-3`
`text{~ Học Tốt Nha ~}`