How can I solve this equation involving two variables?

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To solve the equations 3x^2 + xy - y^2 = 81 and x + y = 7, start by expressing one variable in terms of the other using the simpler equation, x + y = 7. Substitute this expression into the first equation to eliminate one variable. The discussion emphasizes that this approach is basic algebra, not advanced math, and encourages showing work for better assistance. Participants suggest finding y in terms of x or vice versa before substituting back into the original equation. This method will lead to the solution of the system of equations.
Aladin
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please help me in solving this question.
3x^2+xy-y^2=81 ; x+y=7


I will be thankful to you
 
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We don't do your homework here. Show some work, please.
 
Also it's not a question:
"Hey"
-Hey
"3x^2+xy-y^2=81 ; x+y=7 ??"
-Yes
"OK."
 
Aladin said:
please help me in solving this question.
3x^2+xy-y^2=81 ; x+y=7


I will be thankful to you

Hi Aladin! :smile:

Hint: do the easy equation first.

So x = … ? :smile:
 
Find y in terms of x and substitute...
 
this isn't even precalculus its basic algebra
 
it is not my home work I am just trying to solve it because I am learning basic math.so please help me in solving this equation
 
Just follow everyone's advice and solve find x in terms of y or vice versa y in terms of x and substitute back into your equation.
 
after you solve in terms of the other with one equation you have to plug in for the other equation
 

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