(√2+√3)(2-√6+√7)-√21 2√2+2√3-√12-√18+√14+√21-√21
--------------------------------- = ---------------------------------------------- =
√7-1 √7-1
2√2+2√3-2√3-3√2+√14 √14-√2 √2(√7-1)
= --------------------------------- = ------------- = ----------- = √2
√7-1 √7-1 √7-1