m=1/3a(a+1)*(a+2),n=1/3(a-1)*a*(a+1),那么m-n=

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m=1/3a(a+1)*(a+2),n=1/3(a-1)*a*(a+1),那么m-n=
m=1/3a(a+1)*(a+2),n=1/3(a-1)*a*(a+1),那么m-n=

m=1/3a(a+1)*(a+2),n=1/3(a-1)*a*(a+1),那么m-n=
a*(a+1)

m-n
=1/3a(a+1)*(a+2)-1/3(a-1)*a*(a+1)
=1/3a(a+1)*[(a+2)-(a-1)]
=a(a+1)

=1/3a(a+1)[(a+2)-(a-1)]
=1/3a(a+1)(3)
=a(a+1)
=a^2+a

解:m-n=(a-1)/3(a-1)*a*(a+1)*(a+2)-(a+2)/3(a-1)*a*(a+1)*(a+2)
=-1/(a-1)*a*(a+1)*(a+2)

m=1/3a(a+1)×(a+2),n=1/3(a-1)×a×(a+1),
那么m-n=1/3a(a+1)×(a+2-a+1)=a(a+1)