Question

[Cô gái xinh đẹp]

Tìm x,y thuộc N biết 

xy = 30

x ( y +2 ) = 15

xy + 7y + x =19

Answer 1

[Băng Dii~]

xy = 30

=> \(x,y\in\)Ư(30)

=> \(x,y\in\left\{1;2;3;5;6;10;15;30\right\}\)

x ( y + 2 ) = 15

=> x, y+ 2 \(\inƯ\left(15\right)\)

= \(x,y+2\in\left\{1;3;5;15\right\}\)

Answer 2

[Uchiha Sasuke]

\(xy=30\)
\(\Rightarrow\left(x,y\right)=\left(1,30\right);\left(30,1\right);\left(5,6\right);\left(6,5\right);\left(15,2\right);\left(2,15\right);\left(3,10\right);\left(10,3\right)\)
\(x\left(y+2\right)=15\)
\(\Rightarrow\)Ta có bảng sau :
 

y+2	3	5	1	15
y	1	3	y\(\notin\)N	13
x	5	3	15	1

xy + 7y  + x = 19
\(\Rightarrow\)y(x+7) + x + 7 = 26
\(\Rightarrow\)( x + 7 ) ( y + 1) = 26
\(\Rightarrow\)ta có bảng sau :

x+7	1	26	2	13
y+1	26	1	13	2
x	\(x\notin N\)	19	\(x\notin N\)	6
y	25	\(y\notin N\)	12	\(y\notin N\)