(9.8-1.8x)×7=18.22.6x=51.6-3.4x3(4x-2)-2(3x+3)=9-8x20+4x=6x-245(x-1)=x+13(3x-2)=10-0.5(x-3.5)0.4(x-0.2)+1.5=0.7x-0.38(0.6x+420)÷(x+20)=335(2-x)+15(6-5x)=22x+7+21(4-3x)

问题描述:

(9.8-1.8x)×7=18.2
2.6x=51.6-3.4x
3(4x-2)-2(3x+3)=9-8x
20+4x=6x-24
5(x-1)=x+1
3(3x-2)=10-0.5(x-3.5)
0.4(x-0.2)+1.5=0.7x-0.38
(0.6x+420)÷(x+20)=3
35(2-x)+15(6-5x)=22x+7+21(4-3x)


(1)(9.8-1.8x)×7=18.2,
  (9.8-1.8x)×7÷7=18.2÷7,
            9.8-1.8x=2.6,
       9.8-1.8x+1.8x=2.6+1.8x,
            2.6+1.8x=9.8,
        2.6+1.8x-2.6=9.8-2.6,
                1.8x=7.2,
           1.8x÷1.8=7.2÷1.8,
                   x=4;
(2)2.6x=51.6-3.4x,
2.6x+3.4x=51.6-3.4x+3.4x,
       6x=51.6,
    6x÷6=51.6÷6,
        x=8.6;
(3)3(4x-2)-2(3x+3)=9-8x,
                  6x-12=9-8x,
               6x-12+8x=9-8x+8x,
                 14x-12=9,
              14x-12+12=9+12,
                    14x=21,
                14x÷14=21÷14,
                      x=1.5;
(4)20+4x=6x-24,
  20+4x-4x=6x-24-4x,
     2x-24=20,
  2x-24+24=20+24,
        2x=44,
     2x÷2=44÷2,
         x=22;
(5)5(x-1)=x+1,
        5x-5=x+1,
      5x-5-x=x+1-x,
        4x-5=1,
      4x-5+5=1+5,
          4x=6,
       4x÷4=6÷4,
           x=1.5;
(6)3(3x-2)=10-0.5(x-3.5),
         9x-6=11.75-0.5x,
    9x-6+0.5x=11.75-0.5x+0.5x,
       9.5x-6=11.75,
     9.5x-6+6=11.75+6,
         9.5x=17.75,
    9.5x÷9.5=17.75÷9.5,
            x=

47
38

(7)0.4(x-0.2)+1.5=0.7x-0.38,
           0.4x+1.42=0.7x-0.38,
      0.4x+1.42-0.4x=0.7x-0.38-0.4x,
           0.3x-0.38=1.42,
      0.3x-0.38+0.38=1.42+0.38,
                0.3x=1.8,
           0.3x÷0.3=1.8÷0.3,
                   x=6;
(8)(0.6x+420)÷(x+20)=3,
(0.6x+420)÷(x+20)×(x+20)=3×(x+20),
                      3(x+20)=0.6x+420,
                          3x+60=0.6x+420,
                     3x+60-0.6x=0.6x+420-0.6x,
                        2.4x+60=420,
                     2.4x+60-60=420-60,
                           2.4x=360,
                      2.4x÷2.4=360÷2.4,
                              x=150;
(9)35(2-x)+15(6-5x)=22x+7+21(4-3x),
                160-110x=91-41x,
           160-110x+110x=91-41x+110x,
                  69x+91=160,
               69x+91-91=160-91,
                     69x=69,
                 69x÷69=69÷69,
                       x=1.
答案解析:(1)等式的两边同时除以7,然后再根据等式的性质进行解答;
(2)等式的两边同时加上3.4x,然后根据等式的性质进行解答;
(3)去掉括号,把原式改写成6x-12=9-8x,然后根据等式的性质进行解答;
(4)等式的两边同时减去4x,然后根据等式的性质进行解答;
(5)去掉括号,把原式改写成5x-5=x+1,然后根据等式的性质进行解答;
(6)去掉括号,把原式改写成9x-6=11.75-0.5x,然后根据等式的性质进行解答;
(7)去掉括号,把原式改写成0.4x+1.42=0.7x-0.38,然后根据等式的性质进行解答;
(8)等式的两边同时乘上x+20,把原式改写成3(x+20)=0.6x+420,然后根据等式的性质进行解答;
(9)去掉括号,把原式改写成160-110x=91-41x,然后根据等式的性质进行解答.
考试点:方程的解和解方程.
知识点:本题主要考查较难的解方程,要把方程化成一般形式,然后再根据等式的性质进行解答.