计算,x²(x-9)= (2a+1)(a+2)+x²(x-9)= (2a+1)(a+2)=

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计算,x²(x-9)= (2a+1)(a+2)+
x²(x-9)=
(2a+1)(a+2)=

x²(x-9)=x²·x-x²·9=x³-9x²
(2a+1)(a+2)
=2a·a+2a·2+1·a+1·2
=2a²+4a+a+2
=2a²+5a+2