Solve Integer Equation: 3x+5y=2xy-1

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In summary, the given equation is multiplied by 2 and rearranged, resulting in a factorized form of (2x-5)(2y-3) = 17. Since 17 is a prime number, there are only four possible cases for the values of x and y, which are (11,2), (3,10), (-6,1), and (2,-7).
  • #1
kaliprasad
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Solve in integers $3x + 5y = 2xy - 1$
 
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[sp]
Multiply by $2$ and rearrange: $4xy - 6x - 10y = 2.$

Factorise: $(2x-5)(2y-3) = 17.$

Since $17$ is prime, there are just four possible cases:

1) $\quad 2x-5 = 17$, $2y-3 = 1$, giving $(x,y) = (11,2).$

2) $\quad 2x-5 = 1$, $2y-3 = 17$, giving $(x,y) = (3,10).$

3) $\quad 2x-5 = -17$, $2y-3 = -1$, giving $(x,y) = (-6,1).$

4) $\quad 2x-5 = -1$, $2y-3 = -17$, giving $(x,y) = (2,-7).$
[/sp]
 
  • #3
Opalg said:
[sp]
Multiply by $2$ and rearrange: $4xy - 6x - 10y = 2.$

Factorise: $(2x-5)(2y-3) = 17.$

Since $17$ is prime, there are just four possible cases:

1) $\quad 2x-5 = 17$, $2y-3 = 1$, giving $(x,y) = (11,2).$

2) $\quad 2x-5 = 1$, $2y-3 = 17$, giving $(x,y) = (3,10).$

3) $\quad 2x-5 = -17$, $2y-3 = -1$, giving $(x,y) = (-6,1).$

4) $\quad 2x-5 = -1$, $2y-3 = -17$, giving $(x,y) = (2,-7).$
[/sp]

My starting point is different and it becomes same as above

We have $2xy - 3x - 5y - 1 = 2( x - \frac{5}{2}) ( y - \frac{3}{2}) - 1 - \frac{15}{2} = 0$
or $ 2 ( 2x - 5) (2y - 3) = 2 * 17$
or $( 2x - 5) (2y-3) = 17$
Note that LHS is odd and so is RHS.
giving 4 solutions
$2x- 5 = -1, 2y -3= -17$ or $x = 2, y = - 7$
$2x -5 = -17, 2y -3= -1$ or $x = -6, y = 1$
$2x- 5 = 1, 2y -3= 17$ or $x = 3, y = 10$
$2x -5 = 17, 2y -3= -1$ or $x = 11, y = 2$
 

FAQ: Solve Integer Equation: 3x+5y=2xy-1

What is an integer equation?

An integer equation is an equation where the only solutions are integers (whole numbers). This means that when solved, the values of the variables in the equation must be whole numbers, not fractions or decimals.

How is an integer equation different from a regular equation?

Unlike a regular equation, an integer equation has the additional constraint that the solutions must be integers. This makes it more challenging to solve, as the possible solutions are limited.

How do you solve an integer equation?

To solve an integer equation, you need to find values for the variables that make the equation true. This can be done through various methods such as substitution, elimination, or graphing. However, with integer equations, it is important to check that the solutions are integers before considering them as valid solutions.

What is the purpose of solving an integer equation?

Solving an integer equation can help us find the values of the variables that satisfy the given equation. This can be useful in real-life situations, such as in problem-solving and decision-making, where the values must be whole numbers.

Is there a general method for solving all integer equations?

No, there is no one-size-fits-all method for solving integer equations. The method used depends on the specific equation and its variables. Some equations may be easier to solve using one method while others may require a different approach.

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