SOLUTION: Solve the system of equations x^2 + y^2 - x - y = 18 xy + 2x + 2y = 26 I'm really having hard time at this part.

Algebra.Com
Question 983071: Solve the system of equations
x^2 + y^2 - x - y = 18
xy + 2x + 2y = 26
I'm really having hard time at this part.

Found 2 solutions by ikleyn, Edwin McCravy:
Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!

You need to solve the non-linear system of two equations in two unknowns

.

Multiply the second equation by  2  (both sides)  and then add to the first one.  You will get

+ = ,   or

+ - = 0.

The last equation is quadratic for  (x + y)  and has the roots

a) x + y = -10   and   b) x + y = 7.

So,  combining this with the second equation of the original system, you should solve two systems

a)     and     b) .

or

a)     and     b) .

The system  a)  has no real solutions.

The system  b)  has two solutions  x=4, y=3  and  x=3, y=4.

Answer.  Two solutions are  x=4, y=3  and  x=3, y=4.


Answer by Edwin McCravy(20054)   (Show Source): You can put this solution on YOUR website!


Instead of doing your problem for you, I will do one exactly 
in every detail step-by-step like your problem.  All you have
to do is use the problem below as a model. The problem I will
do is:



One thing we observe about this problem is that it is symmetrical
in x and y.  That is we have the same two equations if we interchange
x and y.  Therefore any time we get a pair of solutions for x, one will
be a solution for x and the other will be a solution for y.

Solve the second for y




 

Substitute in the first equation:



Multiply through by (x+2)², [but we know x can't be -2]



Get binomials in descending order:









Looking at the graph on a graphing calculator it appears that 
it has solutions 2 and 5 but it probably has a pair of conjugate
complex solutions too.  We use synthetic division with x=2

2 | 1 1 -6 -200  400
  |   2  6    0 -400 
    1 3  0 -200    0

5 | 1  3   0 -200
  |    5  40  200    
    1  8  40    0

So we have factored the polynomial as



So we have solutions x=2, x=5, 

By the symmetry, we know that when x=2, y=5
and when x=5, y=2.

we get the other solutions from
using the quadratic formula, since it won't factor.

















So the other pair of solutions, by symmetry, are

if , then 

and 

if , then 

Now you do your problem exactly step-by step like I did this one.

Edwin

RELATED QUESTIONS

I am having some trouble with this one. Solve the system of equations. Let z be the... (answered by Edwin McCravy)
I am having a hard time doing this can someone help me Use the substitution method... (answered by solver91311)
I am having a hard time with Matrices and Determinants. Here's the problem I'm having a... (answered by stanbon)
Please help me solve this equation: Solve the system of equations. X - Y + 2z = -3 (answered by Alan3354)
This would be the last time I'd adk... maybe. But I really am having a hard time on... (answered by ikleyn)
solve the following system of equations: x + y + square root(xy) = 28 x^2 + y^2 + xy... (answered by ankor@dixie-net.com)
Hi, my name is Will and I am having a hard time solving systems of linear equations... (answered by MathLover1,MathTherapy)
I'm having a hard time figuring out the following equation's properties: 3(2x)y = (3 × (answered by solver91311)
Solve this system of linear equations: {{{y=x-2}}}... (answered by math-vortex)