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222-9+11+12:2*14+14 = ? ( )

## Toán Lớp 6: tìm x,y thuộc biết a, ( x + 5) . ( y -3 ) = 15

Toán Lớp 6: tìm x,y thuộc biết
a, ( x + 5) . ( y -3 ) = 15

$\text{Vì}$ x , y \in ZZ $\text{nên}$ x + 5 ; y – 3 \in ZZ
=> (x + 5) . (y – 3) \in Ư(15) = {+-1 ; +-3 ; +-5 ; +-15}
$\text{Lập bảng giá trị:}$
$\begin{array}{|c|c|c|}\hline x + 5&1&3&5&15&-1&-3&-5&-15\\\hline y-3&15&5&3&1&-15&-5&-3&-1\\\hline x&-4&-2&0&10&-6&-8&-10&-20\\\hline y&18&8&6&4&-12&-2&0&2\\\hline \text{Thử lại}&\text{TM}&\text{TM}&\text{TM}&\text{TM}&\text{TM}&\text{TM}&\text{TM}&\text{TM}\\\hline\end{array}$
$\text{Vậy}$ (x , y) = (-4 , 18) ; (-2 , 8) ; (0 , 6) ; (10 , 4) ; (-6 , -12) ; (-8 , -2) ; (-10 , 0) ; (-20 , 2)

2. $( x + 5 ) . ( y – 3 ) = 15$
$TH1 :$ $$\left[ \begin{array}{l}x+5=5\\y-3=3\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=0\\y=6\end{array} \right.$$
$TH2 :$ $$\left[ \begin{array}{l}x+5=3\\y-3=5\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-2\\y=8\end{array} \right.$$
$TH3 :$ $$\left[ \begin{array}{l}x+5=-3\\y-3=-5\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-8\\y=-2\end{array} \right.$$
$TH4 :$ $$\left[ \begin{array}{l}x+5=-5\\y-3=-3\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-10\\y=-6\end{array} \right.$$
$TH5 :$ $$\left[ \begin{array}{l}x+5=15\\y-3=1\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=10\\y=4\end{array} \right.$$
$TH6 :$ $$\left[ \begin{array}{l}x+5=1\\y-3=15\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-4\\y=18\end{array} \right.$$
$TH7 :$  $$\left[ \begin{array}{l}x+5=-15\\y-3=-1\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-20\\y=2\end{array} \right.$$
$TH8 :$ $$\left[ \begin{array}{l}x+5=-1\\y-3=-15\end{array} \right.$$
$⇒$ $$\left[ \begin{array}{l}x=-6\\y=-12\end{array} \right.$$