7c:
x+2/327 + x+3/326 + x+4/325 + x+5/324 + x+349/5 = 0
(x+2+327/327) + (x+3+326/326) + (x+4+325/325) + (x+5+324/324) + (x+349-5-5-5-5/5) = 0
x+329/327 + x+329/326 + x+329/325 + x+329/324 + x+329/5=0
x+329(1/327 + 1/326 + 1/325 + 1/324 + 1/5) = 0
=> x+329 = 0
=> x = -329
Vậy x=-329.
B8:
e, 2x+y-xy=5
x(2-y)+y-4=1
x(2-y)-2(2-y)=1
(x-2)(2-y)=1
=> x-2,2-y ∈ Ư(1)
=> (x-2;2-y) là (1;1);(-1;-1)
=> (x;y) là (3;1);(1;3)
Vậy (x;y) là (3;1);(1;3).
d, xy - 2x - 3y = 11
x(y-2) - 3y - 6 = 5
x(y-2) - 3(y-2) = 5
(x-3)(y-2) = 5
=> x-3,y-2 ∈ Ư(5)
=> (x-3;y-2) là (1;5);(-1;-5);(-5;-1);(5;1)
=> (x;y) là (4;7);(2;-3);(-2;1);(8;3)
Vậy (x;y) là (4;7);(2;-3);(-2;1);(8;3).
