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b) xy + x - y = 4
<=> ( xy + x ) - ( y + 1 ) = 3
<=> x(y + 1 ) - ( y + 1 ) = 3
<=> ( y + 1 ) ( x - 1 ) = 3
Theo bài ra cần tìm các số nguyên dương x,y => Xét các trường hợp y + 1 nguyên dương và x - 1 nguyên dương
Mà 3 = 1 x 3 => Chỉ cs thể xảy ra 2 th :
* TH1 : y + 1 = 1 ; x -1 = 3 => y = 0 , x = 4 ( loại vì y = 0 )
* TH2 : y + 1 = 3 ; x -1 = 1 => y = 2 ; x = 2 ( T/m )
Vậy x = y = 2
c) xy + 12 = x + y
Ta có :
xy + 12 = x + y
xy - x - y = 12
x.( y -1 ) - y = 12
[ x.(y -1 ) - y ] + 1 = 12 + 1
. ( y - 1 ) - ( y -1 ) = 13
( x - 1 ) . ( y - 1 ) = 13
=> x - 1 và y - 1 thuộc Ư( 13)
Mà Ư(13 ) = { -13 ; -1 ; 1 ; 13 }
Ta có bảng :\
x -1 | x | y-1 | y |
-13 | -12 | -1 | 0 |
-1 | 0 | -13 | -12 |
1 | 2 | 13 | 14 |
13 | 14 | 1 | 2 |
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mình ko chép đề bài nha
a) \(\dfrac{16}{5}\): \(\dfrac{7}{3}\) : y =\(\dfrac{12}{7}\)
\(\dfrac{48}{35}\): y = \(\dfrac{12}{7}\)
y = \(\dfrac{48}{35}\): \(\dfrac{12}{7}\)
y = \(\dfrac{4}{5}\)
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\(\frac{4y}{3}+\frac{2y}{3}+8y=150\)
\(\frac{6y}{3}+8y=150\)
\(2y+8y=150\)
\(10y=150\)
\(y=15\)
vậy \(y=15\)
y x (4/3+2/3+8)=150
y x 10 = 150
y = 150 : 10 = 15
k mk nha
![](https://rs.olm.vn/images/avt/0.png?1311)
y : 3 . 4 + y : 3 . 2 + y . 8 = 150
4/3y + 2/3y + 8y = 150
10y = 150
y = 150 : 10
y = 15
y : 3 x 4 + y : 3 x 2 + y x 8 = 150
y x 1/12 + y x 1/6 + y x 8 = 150
y x ( 1/12 + 1/6 + 8 ) = 150
y x 8.25 = 150
y = 150 : 8.25
y = 18,(18)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{2}{5}\) x y : \(\dfrac{7}{4}\) = \(\dfrac{7}{8}\)
\(\dfrac{2}{5}\) x y = \(\dfrac{7}{8}\) x \(\dfrac{7}{4}\)
\(\dfrac{2}{5}\) x y = \(\dfrac{49}{32}\)
y = \(\dfrac{49}{32}\) : \(\dfrac{2}{5}\)
y = \(\dfrac{245}{64}\)
2\(\dfrac{2}{5}\): y x 1\(\dfrac{1}{4}\) = 2\(\dfrac{3}{5}\)
\(\dfrac{12}{5}\): y x \(\dfrac{5}{4}\) = \(\dfrac{13}{5}\)
\(\dfrac{12}{5}\): y = \(\dfrac{13}{5}\): \(\dfrac{5}{4}\)
\(\dfrac{12}{5}\): y = \(\dfrac{52}{25}\)
y = \(\dfrac{12}{5}\): \(\dfrac{52}{25}\)
y = \(\dfrac{15}{13}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
12:(y x 3)=4
y+3=12:4
y+3=3
y =3-3
y=0
k cho mk nha
12 : ( y x 3 ) = 4
y x 3 = 12 : 4
y x 3 = 3
y = 3 : 3
y = 1
Học tốt nha bạn