X^2+(x+1)^2=(x+2)^2
2x^2+2x+1=(x+2)^2
2x^2+2x+1x^2+4x+4
x^2-2x-3=0
(x-3)(x+1)=0
x-3=0 x+1=0
x=3 x+1=0
x=3 x=-1
6(1 - Cos²x) - Cosx - 5 = 0
6 - 6Cos²x - Cosx -5 = 0
6Cos²x + Cosx -1 = 0
D = 25
Cosx = (-1+5)/12= 1/3 б) Cosx = (-1 -5)/12 = -1/2
x = +-arcCos1/3 + 2πk, k ∈Z x = +-2π/3+ 2πn, n ∈Z