Đáp án+Giải thích các bước giải:
`x=2+\sqrt{3}`
`=>x^2=(2+\sqrt{3})^2=4+3+2.2\sqrt{3}=7+4\sqrt{3}`
`->x^3=(7+4\sqrt{3})(2+\sqrt{3})=14+7\sqrt{3}+8\sqrt{3}+12`
`=26+15\sqrt{3}`
`=>x^4=(26+15\sqrt{3})(2+\sqrt{3})=52+26\sqrt{3}+30\sqrt{3}+45`
`=97+56\sqrt{3}`
`=>A=\frac{97+56\sqrt{3}-2(26+15\sqrt{3})+3(7+4\sqrt{3})-38(2+\sqrt{3})+5}{\sqrt{7+4\sqrt{3}-4(2+\sqrt{3})+5}}`
`=\frac{102+56\sqrt{3}-52-30\sqrt{3}+21+12\sqrt{3}-76-38\sqrt{3}}{\sqrt{12+4\sqrt{3}-8-4\sqrt{3}}}`
`=\frac{-5}{\sqrt{4}}`
`=-5/2`
