Cho a,b,c > 0:abc=1

Cmr: 1a2+2b2+3+1b2+2c2+3+1c2+2a2+312\dfrac{1}{a^2+2b^2+3}+\dfrac{1}{b^2+2c^2+3}+\dfrac{1}{c^2+2a^2+3}\le\dfrac{1}{2}

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