B + Y’ = 2COS 22− X 0

2.b + y’ = ^{2cos 2}

₂

− x 0.5

sin 2

+ y’ = 0 ⇔ cos2x = 0 ⇔ x = ^π ₄ ^{+ k π} ₂ ( ^{k Z ∈} ) ^0.5