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求未知数x的值:x+ 1 2 x= 4 5 ...

①2x:(1-x)=45 2x=(1-x)×45 2x=(1-x)×0.8 2x=0.8-0.8x 2x+0.8x=0.8-0.8x+0.8x 2.8x=0.8 2.8x÷2.8=0.8÷2.8 x=27②12-2.5x=412-2.5x+2.5x=4+2.5x 12=4+2.5x 4+2.5x=12 4+2.5x-4=12-4 2.5x=8 2.5x÷2.5=8÷2.5 x=3.2.

(1)x8=4.512, 12X=8×4.5, 12X÷12=36÷12, X=3;(2)х+14х=60,(1+14)х=60, 54х=60, 54х×45=60×45, X=48.

①49+40%x=89 49+40%x-49=89-49 0.4x=40 0.4x÷0.4=40÷0.4 x=100;②15:x=14:4 14x=15×4 14x×4=60×4 x=240;③16:25=12:x 16x=25×12 16x=15 16x×6=15×6 x=115;

x-3/5+1/2=3/4 x=3/4+3/5-1/2 x=15/20+12/20-10/20 x=17/20

(1)135:4=x:2.5, 4x=1.6×2.5, 4x=4, 4x÷4=4÷4, x=1;(2)x2.8=40.7, 0.7X=2.8×4,0.7X÷0.7=11.2÷0.7, X=16;(3)0.12×5-12x=35, 0.6-12x=35, 0.6-0.5x+0.5x=0.6+0.5x, 0.6+0.5x=0.6, 0.6+0.5x-0.6=0.6-0.6, 0.5x=0, x=0;(4...

将未知数的值代入方程(1)x2+4x-5=0,(5,1),检验得:1是根,5不是根;故本题答案为1是根,5不是根.(2)2y2-5y+2=0,(1,12),检验得:12是根,1不是根.故本题答案为12是根,1不是根.

。(1)4x+5分之1=3分之2 4x+1/5=2/3 方程两边乘以15 60x+2=10 60x=10-2 60x=8 x=2/15 (2)4分之5×9-6x=4 5/4*9-6x=4 方程两边乘以4 45-24x=16 -24x=16-45 -24x=-29 x=29/24

把x=1代入方程px+5q=97可得:p+5q=97,故p与5q中必有一个为偶数,①若p=2,则5q=95,q=19,40p+101q+4=2003.②若5q为偶数,则q为2,p=87,而87不是质数,与题意矛盾.综上可得:40p+101q+4=2003.故答案为:2003.

42÷12+x=5求未知数x 解:3.5+x=5 x=5-3.5 x=1.5

(3/7+x)÷(1/5)=6 3/7+x=6×(1/5) x=6/5-3/7 =42/35-15/35 =27/35

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