a) с₉ = 17 d = 2 c₁ = ?
c₉ = c₁ + 8d
c₁ = c₉ - 8d = 17 - 8 * 2 = 17 - 16 = 1
б) c₄ = 7 c₉ = - 8 c₁ = ?
c₁ = 7 - 3d = 7 - 3 * (- 3) = 7 + 9 = 16
y+6/y-6 - у+2/у+6= (у+6)^2/(у^2 - 6^2) - (у+2)(у-6)/(у^2 - 6^2) = у^2+ 12у + 36 - у^2 + 6у - 2у + 12/ у^2 - 36 = 16у - 48/ у^2- 36
(a²-1)/(a-b) *(7a-7b)/(a²+a) =(a-1)(a+1)*7(a-b) /(a-b)*a(a+1) =7(a-1) /a =(7a -7) /a
2a²-6ab=2a(a-3b)
x³-49x=x(x-7)(x+7)
(√7+1)²=7+1=8
(4√5-5√2)²=(16*5)-(25*2)=30