1) (b+√c)(b-√c) = b² -√c²=b² -c
2) (√x-√y)(√x+√y)= √x² - √y² = x - y
3) (√15-2)(2+√15)= (√15)² -2² = 15 -4 = 11
4) (1+3√2)(3√2-1) (3√2)² - 1² = 18 - 1= 17
5) (5√3-√11)(√11+5√3)=(5√3)² - (√11)² = 75 - 11 =64
6) (a+√b)² = a² + 2a√b +b
7) (√x-√y)² = x - 2√(xy) +y
8) (√3-√6)² = 3 - 2 √(3· 6) + 6 = 9 -√18 =9 - 3√2
9) (1-2√3)² = 1 - 2·1·2√3 +(2√3)² = 1 - 4√3 + 12 = 13 - 4√3
10) (3√5+2√10)²= (3√5)²+ 2·3√5·2√10+(2√10)² =45 + 60√2 +40 = 85 + 60√2