一(一1/3+m2次方n+m3次方)一(2/3一m2次方n一m3次方)
=1/3-m2次方n-m3次方-2/3+m2次方n+m3次方
=1/3-2/3-m2次方n+m2次方-m3次方n+m3次方
=1/3-2/3
=-1/3
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