關於開方的數學題

1)
1 / (1 - √6)
= (1 + √6) / [(1 - √6)(1 + √6)]
= - (1 + √6) / 5

2)
18 / (√18 + 2)
= 18(√18 - 2) / [(√18 + 2)(√18 - 2)]
= 18(3√2 - 2) / (18 – 4)
= 9(3√2 - 2) / 7

3)
3√6 / (√17 - √15)
= 3√6 (√17 + √15) / [(√17 + √15)(√17 - √15)]
= 3√6 (√17 + √15) / 2

4)
(2√2 - √3) / [3(2√2 + √3)]
= (2√2 - √3)(2√2 - √3) / [3(2√2 + √3)(2√2 - √3)]
= (8 - 4√6 + 3) / [3(5)]
= (11 - 4√6) / 15

1. -√16
2. √18+2
3. 3√3
4. 1/3