令3.15+2.17+5.61=x
令2.17+5.61=y
所以原式变成
x(y+6.6)-(x+6.6)y
=xy+6.6x-xy-6.6y
=6.6(x-y)
=6.6×[(3.15+2.17+5.61)-(2.17+5.61)]
=6.6×3.15
=20.79
(3.15+2.17+5.61）×(2.17+5.61+6.6)-（3.15+2.17+
1个回答
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