Problem: Find all real solutions to the system of equations {x(y−1)+y(x+1)=6(x−1)(y+1)=1
Solution
Solution: Let us first expand and simplify the equations.
From the first equation: x(y−1)+y(x+1)=6 Expand: xy−x+yx+y=6 Combine like terms: xy−x+xy+y=6 2xy−x+y=6
From the second equation: (x−1)(y+1)=1 Expand: xy+x−y−1=1 xy+x−y=2
Now, let us solve the system:
We have: 1) 2xy−x+y=6 2) xy+x−y=2
Let us add the two equations:
Equation 1: 2xy−x+y=6 Equation 2: xy+x−y=2
Let us try to eliminate variables. Add equation 1 and equation 2:
But first, let's try to express one variable in terms of the other.
From equation 2: xy+x−y=2 xy−y=2−x y(x−1)=2−x If x=1, y=x−12−x
Now substitute this value of y into equation 1: 2xy−x+y=6 Substitute y: 2x(x−12−x)−x+x−12−x=6 Multiply both sides by x−1 (assuming x=1): 2x(2−x)−x(x−1)+(2−x)=6(x−1) Expand: 2x(2−x)=4x−2x2 −x(x−1)=−x2+x So: 4x−2x2−x2+x+2−x=6x−6 Combine like terms: −2x2−x2=−3x2 4x+x−x=4x So: −3x2+4x+2=6x−6 Bring all terms to one side: −3x2+4x+2−6x+6=0 −3x2−2x+8=0 Multiply both sides by −1: 3x2+2x−8=0 Now solve this quadratic equation: x=6−2±4+96=6−2±100=6−2±10 So: x1=6−2+10=68=34 x2=6−2−10=6−12=−2 Now, recall y=x−12−x.
For x=34: y=34−12−34=34−336−4=3132=2 For x=−2: y=−2−12−(−2)=−34=−34
Therefore, the real solutions are: (x,y)=(34,2),(x,y)=(−2,−34)
Check for x=1: From above, y=x−12−x is undefined for x=1, so no solution for x=1.
Final Answer: All real solutions are: (34,2),(−2,−34)
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