Đáp án`+`Giải thích các bước giải:

 `a, (2/(\sqrt{3} - 1) + 3/(\sqrt{3} - 2) +(15)/(3 - \sqrt{3})) . 1/(\sqrt{3} + 5)`

`= ((2(\sqrt{3} + 1))/((\sqrt{3} - 1)(\sqrt{3} + 1)) + (3(\sqrt{3} + 2))/((\sqrt{3} - 2)(\sqrt{3} + 2)) + (15(3 + \sqrt{3}))/((3 -\sqrt{3})(3 + \sqrt{3}))).  1/(\sqrt{3} + 5)`

`= ((2(\sqrt{3} + 1))/(3 - 1) + (3(\sqrt{3} + 2))/(3 - 4) + (15(3 + \sqrt{3}))/(9 - 3)) . 1/(\sqrt{3} + 5)`

`= ((2(\sqrt{3} + 1))/2 + (3(\sqrt{3} + 2))/(-1) + (15(3 + \sqrt{3}))/6) . 1/(\sqrt{3} + 5)`

`= (\sqrt{3} + 1 - 3(\sqrt{3} + 2) + (5(3+\sqrt{3}))/2). 1/(\sqrt{3} + 5)`

`= (\sqrt{3} +1 - 3\sqrt{3} - 6 + (15 + 5\sqrt{3})/2) . 1/(\sqrt{3} + 5)`

`= (-2\sqrt{3} - 5 + (15+ 5\sqrt{3})/2) . 1/(\sqrt{3} + 5)`

`= (-4\sqrt{3} - 10 + 15 + 5\sqrt{3})/2 . 1/(\sqrt{3} + 5)`

`= (5 + \sqrt{3})/2.  1/(\sqrt{3} + 5)`

`= 1/2`

`***`sharksosad