7√3 + 2√27 - √75 =7√3 +2√(9*3) - √(25*3)=
= 7√3 + 2√(3²*3) - √(5²*3)= 7√3 +6√3 - 5√3 =
=(7+6 - 5) *√3= 8√3
2√7 ×√21 = √(4*7) * √21 =√(28*21) = √588 = √(14²*3)= 14√3
(2√2 - √50) *√2 = (2√2 - 5√2 ) * √2 = -3*(√2)² =- 3 * 2 = - 6
(4√80 -√125) : √3 = (4√(16*5) - √(25*5) ) : √3 = (16√5 - 5√5):√3 =
= 11√5 / √ 3 = (11√5 * √3 )/ (√3)² = (11√15)/3
(√(аb+ V ) / √7 = (1/7) * √(7ab +7V)