Question

Tìm x,y ∈ Z biết :

(x+1) + (x+3) + (x+5) + . . . + (x + 99) = 0 (x – 3)(2y + 1) = 7 (x – 7)(x + 3) < 0 3x + 4y – xy = 15

Answer 1

a: \(\left(x+1\right)+\left(x+3\right)+...+\left(x+99\right)=0\)

\(\Leftrightarrow50x+2500=0\)

=>50x=-2500

hay x=-50

c: (x-7)(x+3)<0

=>x+3>0 và x-7<0

=>-3<x<7

b: (x-3)(2y+1)=7

\(\Leftrightarrow\left(x-3;2y+1\right)\in\left\{\left(1;7\right);\left(7;1\right);\left(-1;-7\right);\left(-7;-1\right)\right\}\)

hay \(\left(x,y\right)\in\left\{\left(4;3\right);\left(10;0\right);\left(2;-4\right);\left(-4;-1\right)\right\}\)