Question

已知M-n=5,mn=3,求-(m+4n-mn)-(2mn-2m-3n)+(2n-2m-3mn)的值

Answer 1

原式=-m-4n+mn-2mn+2m+3n+2n-2m-3mn
=-m+n-4mn
=-(m-n)-4mn
=-5-12
=-17

Answer 2

an=2n-4
所以bn-b(n-1)=2n-4
……
b2-b1=0
所以相加
bn-b1=0+2+4+……+（2n-4)=(2n-4)(n-1)/2=n²-3n+2
bn=n²-3n-2