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Tuesday, January 4, 2022

2022/003) Prove x^2+y^2+5>xy+x+3y

 We have

(x-y)^2 >=0 or x^2 + y^2 >=2xy

(x-1)^2 >=0 or x^2 + 1 >= 2x

(y-3)^2 >= 0 or y^2 + 9 >= 6y

Adding we get 2(x^2+y^2 + 5) >= 2(xy+x + 3y)

Or x^2+y^2 + 5 >= xy + x + 3y

This is equal when x = y, y = 3, x= 1 which canot be true so  x^2+y^2 + 5 > xy + x + 3y

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