1. (sqrt(42\5) - sqrt(21\10)):sqrt(105\8) =
= sqrt(42*8\5*105) - sqrt(21*8\10*105) = sqrt(336\525) - sqrt(168\1050) =
= sqrt(1\1.5625) - sqrt(1\6.25) = 1\1.25 - 1\ 2.5 = 1\2.5 = 10\25 = 2\5
2. Безлимитный - 1150
"500" - 500 + (1200-800)*1.5 = 500 + 600 = 1100
"750" - 750 + (1200-1000)*1.2 = 750 + 240 = 990 - самый выгодный