求未知数x. 4x+7.1=12.5-2x 21x=2167
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求未知数x.
4x+7.1=12.5-2x | 21x=
(1)4x+7.1=12.5-2x,
4x+7.1+2x=12.5-2x+2x, 6x+7.1=12.5, 6x+7.1-7.1=12.5-7.1, 6x=5.4, 6x÷6=5.4÷6, x=0.9, (2)21x= 21 67: 9 67, 21x= 21 67÷ 9 67, 21x÷21= 21 67÷ 9 67÷21, x= 21 67× 67 9× 1 21, x= 1 9; (3)1 3 7:0.8=x:14%, 0.8x=1 3 7×14%, 4 5x= 10 7× 7 50, 4 5x× 5 4= 10 7× 7 50× 5 4, x= 1 4. |