Toán Lớp 7: tìm x,y biết a. 2xy+2x+3y=12 b.3/x+2/3=y/2

Question

Toán Lớp 7:  tìm x,y biết  a. 2xy+2x+3y=12 b.3/x+2/3=y/2

giahan44 · Answer

đ&aacute;p &aacute;n + giải th&iacute;ch :   a. Ta c&oacute; :          2    x    y    +    2    x    +    3    y    =    12     2xy+2x+3y=12            &hArr;     &hArr;          (     2    x    y    +    2    x     )     +     (     3    y    +    3     )     =    12    +    3     (2xy+2x)+(3y+3)=12+3    ( cộng hai vế cho 3 )          &hArr;     &hArr;         2    x     (     y    +    1     )     +    3     (     y    +    1     )     =    15     2x(y+1)+3(y+1)=15            &hArr;     &hArr;          (     2    x    +    3     )      (     y    +    1     )     =    15.               b.               x    &minus;    3    =    y    .     (     x    +    2     )      x&minus;3=y.(x+2)            &rArr;     (     x    +    2     )     &minus;    5    =    y    .     (     x    +    2     )      &rArr;(x+2)&minus;5=y.(x+2)            &rArr;     (     x    +    2     )     &minus;    5    &minus;    y    .     (     x    +    2     )     =    0     &rArr;(x+2)&minus;5&minus;y.(x+2)=0            &rArr;     (     x    +    2     )      (     1    &minus;    y     )     =    5.