Toán Lớp 6: a)(2x+1).(3y-2)=-55 b)xy-3x-2y=11 c)xy+3x-7y=21

Question

Toán Lớp 6:  a)(2x+1).(3y-2)=-55 b)xy-3x-2y=11 c)xy+3x-7y=21

hienchaudiem · Answer

Lời giải và giải thích chi tiết:   a, (2x + 1)(y &ndash; 5) = 12   Theo đề b&agrave;i ta c&oacute; 2x+1)(y-5)=12=>2x+1;y-5 thuộc Ư(12)={1;-1;2;-2;3;-3;4;-4;6;-6;12;-12}M&agrave; 2x+1 l&agrave; số nguy&ecirc;n lẻ=>2x+1 thuộc{1  ;  -1;3;-3}=>y-5    thuộc{12;-12;4;-4}=>x thuộc {0;-1;1;-2}=>y thuộc {17;4;9;1}         b    )    2      x      2      &minus;    2    x    y    +    x    &minus;    y    =    12     b)2x2&minus;2xy+x&minus;y=12            &hArr;    2    x     (     x    &minus;    y     )     +     (     x    &minus;    y     )     =    12     &hArr;2x(x&minus;y)+(x&minus;y)=12            &hArr;     (     x    &minus;    y     )      (     2    x    +    1     )     =    12     &hArr;(x&minus;y)(2x+1)=12            &rArr;     (     x    &minus;    y     )     ;     (     2    x    +    1     )     &isin;       Ư        (    12    )      &rArr;(x&minus;y);(2x+1)&isin;Ư(12)            &rArr;       Ư        (    12    )     &isin;     {     &minus;    1    ;    1    ;    &minus;    2    ;    2    ;    &minus;    3    ;    3    ;    &minus;    4    ;    4    ;    &minus;    6    ;    6    ;    &minus;    12    ;    12     }      &rArr;Ư(12)&isin;{&minus;1;1;&minus;2;2;&minus;3;3;&minus;4;4;&minus;6;6;&minus;12;12}      V&igrave; 2x+1 lu&ocirc;n lẻ         &rArr;    2    x    +    1    &isin;     {     &minus;    1    ;    1    ;    &minus;    3    ;    3     }      &rArr;2x+1&isin;{&minus;1;1;&minus;3;3}            &hArr;     hept       {         2    x    +    1    =    &minus;    1          x    &minus;    y    =    &minus;    12              &hArr;     hept       {         x    =    &minus;    1          y    =    11               &hArr; hept{2x+1=&minus;1x&minus;y=&minus;12&hArr; hept{x=&minus;1y=11            &hArr;     hept       {         2    x    +    1    =    1          x    &minus;    y    =    12              &hArr;     hept       {         x    =    0          y    =    &minus;    12               &hArr; hept{2x+1=1x&minus;y=12&hArr; hept{x=0y=&minus;12            &hArr;     hept       {         2    x    +    1    =    &minus;    3          x    &minus;    y    =    &minus;    4              &hArr;     hept       {         x    =    &minus;    2          y    =    2               &hArr; hept{2x+1=&minus;3x&minus;y=&minus;4&hArr; hept{x=&minus;2y=2            &hArr;     hept       {         2    x    +    1    =    3          x    &minus;    y    =    4              &hArr;     hept       {         x    =    1          y    =    &minus;    3