Cosx = - 1/2
x = (+ -)*arccos(-1/2) + 2πk, k∈Z
x = (+ -)*(π - arccos(1/2) + 2πk, k∈Z
x = (+ -)*(π - π/3) + 2πk, k∈Z
x = (+ -)*(2π/3) + 2πk, k∈Z
Xy-9x-2*(x+2xy)=x²y-9x²-2x+2x²y²-18x²y-4xy=2x²y²-17x²y-9x²-2x-4xy=x(2xy²-17xy-9x-2-4y).
94²-37² ∨ 93²-36²
(94-37)(94+37) ∨ (93-36)(93+36)
57*131 ∨ 57*129
57*131 >57*129 ⇒
94²-37² > 93²-36².