1)

8√3-5√12+4√75  = 8√3 - 5√(4*3) + 4√(25*3) =

= 8√3 - 5*2√3 + 4*5√3 = 8√3 - 10√3 + 20√3 = 18√3,

2)

(2√7+3)² = (2√7)² + 2 *2√7 *3 + 3² =

= 4*7 + 4√7 + 9 = 37 + 4√7,

3)

(7√2-3√3)(7√2+3√3) = (7√2)² - (3√3)² = 49*2 - 9*3 =

= 98 - 27 = 71