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共1个回答
热心网友
x1^2+x2^2+x1x2
=x1^2+1/4x2^2+3/4x2^2+x1x2
=(x1^2+x1x2+1/4x2^2)+3/4x2^2
=(x1+1/2x2)^2+3/4x2^2