已知3a-b-4=2.5,求3.9a-1.3b+4.25的值,要列式.

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已知3a-b-4=2.5,求3.9a-1.3b+4.25的值,要列式.
已知3a-b-4=2.5,求3.9a-1.3b+4.25的值,要列式.

已知3a-b-4=2.5,求3.9a-1.3b+4.25的值,要列式.
3a-b-4=2.5
∴3a-b=6.5
3.9a-1.3b+4.25
=1.3*(3a-b)+4.25
=1.3*6.5+4.25
=12.7

3.9a-1.3b+4.25
=1.3(3a-b-4)+1.3*4+4.25
=1.3(3a-b-4)+9.45
=3.25+9.45
=12.7

因为3a-b-4=2.5,所以3a-b=6.5,两边同时乘以1.3得到3.9a-1.3b=8.45,所以3.9a-1.3b+4.25=12.7

由 3a-b-4=2.5得:3a-b=6.5 所以
3.9a-1.3b+4.25=1.3(3a-b)+4.25=12.7