giải giúp mình vs thanks mn nhìu lắm ạ

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`a,`

`a^2 +2a+b^2 +1`

`= a^2 + 2 . a . 1 +1^2 +b^2`

`=(a+1)^2 + b^2 ≥ 0∀a,b`

`-> a^2 + 2a + b^2+1 ≥0∀a,b`

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`b,`

`x^2 + y^2 +2xy + 4`

`= x^2 + 2xy + y^2 + 4`

`= (x+y)^2 + 4 ≥4 > 0∀x,y`

`-> x^2 + y^2 + 2xy + 4 > 0∀x,y`

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`c,`

`(x-3)(x-5)+2`

`= x^2 - 5x - 3x + 15+2`

`=x^2 - 8x + 17`

`=x^2 - 2 . x . 4 + 4^2 +1`

`= (x-4)^2 + 1 ≥1 > 0∀x`

`-> (x-3)(x-5) + 2 > 0∀x`