The proof of inequality, Verification: A ^ 2 + B ^ 2 + C ^ 2 ≥ AB + BC + Ca

This question can be verified indirectly
A ^ 2 + B ^ 2 > = 2Ab is obtained from (a-b) ^ 2 > = 0
Similar results can be obtained
(a-c)^2>=0
a^2+c^2>=2ac
(b-c)^2>=0
b^2+c^2>=2bc
Add up the three inequalities to get the result
a^2+b^2+c^2>=ab+ac+bc

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