If and are positive real numbers with and and are solutions to the system below, what is the greatest lower bound of ?
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If we solve the system for x and y , we get:
x = a b ( a + b ) a 2 + a b + b 2 and y = − a + b 1
Therefore, ∣ ∣ ∣ ∣ y x ∣ ∣ ∣ ∣ = a b a 2 + a b + b 2 = 1 + b a + a b . But b a + a b ≥ 2 by AM-GM, so the minimum possible value for ∣ ∣ ∣ ∣ y x ∣ ∣ ∣ ∣ is 1 + 2 = 3 .