设M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),那么M-N=A a²+a B (a+1)(a+2) C 1/3a²+1/3a D 1/3(a+1)(a+2)

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设M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),那么M-N=A a²+a B (a+1)(a+2) C 1/3a²+1/3a D 1/3(a+1)(a+2)

设M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),那么M-N=A a²+a B (a+1)(a+2) C 1/3a²+1/3a D 1/3(a+1)(a+2)
设M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),那么M-N=
A a²+a B (a+1)(a+2) C 1/3a²+1/3a D 1/3(a+1)(a+2)

设M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),那么M-N=A a²+a B (a+1)(a+2) C 1/3a²+1/3a D 1/3(a+1)(a+2)
M=1/3a(a+1)(a+2),N=1/3a(a-1)(a+1),
M-N=1/3a(a+1)(a+2)-1/3a(a-1)(a+1)
=1/3a(a+1)[(a+2)-(a-1)]
=1/3a(a+1)[2+1]
=(1/3)*3*a(a+1)
=a(a+1)
=a²+a
答案A