Решение
№ 2.
√28(√14 - √7) - 2√98 = √14*√2*(√14 - √7) - 2√14√7 = 14√2 - 14 - 14√2 = - 14
№ 3.
x - 4y = 3
x² - 21y = 28
x = 4y + 3
(4y + 3)² - 21y = 28
16y² + 24y + 9 - 21y - 28 = 0
16y² + 3y - 19 = 0
D = 9 + 4*16*19 = 1225
y₁ = (- 3 - 35)/32 = - 38/32 = - 19/16
y₁ = - 1 (3/16)
y₂ = (- 3 + 35)/32 = 1
x₁ = 4*(- 19/16) + 3
x₁ = - 19/4 + 3
x₁ = - 7/4
x₁ = - 1,75
x₂ = 4*1 + 3
x₂ = 7
Ответ: ( - 1,75 ; - 1(3/16)) ; ( 7 ; 1)