SOLUTION: Solve the problem of equations by substitution method X+7y=31 2x+3y=7

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Question 1051834: Solve the problem of equations by substitution method
X+7y=31
2x+3y=7
Found 2 solutions by ikleyn, solver91311:
Answer by ikleyn(52777) About Me  (Show Source):
You can put this solution on YOUR website!
.
Solve the problem of equations by substitution method 

 x + 7y = 31   (1)
2x + 3y =  7   (2)

From (1), express x = 31-7y, and then substitute it into (2). You will get

2*(31-7y) + 3y = 7.

Simplify:

62 - 14y + 3y = 7,

-14y + 3y = 7 - 62,

-11y = -55,

y = %28-55%29%2F%28-11%29 = 5.

Then x = 31-7y = 31-7*5 = 31-35 = -4.

Answer.  x = -4, y = 5.

On solving systems of linear equations in two unknowns see the lessons
    - Solution of a linear system of two equations in two unknowns by the Substitution method
    - Solution of a linear system of two equations in two unknowns by the Elimination method
    - Solution of a linear system of two equations in two unknowns using determinant
    - Geometric interpretation of a linear system of two equations in two unknowns
    - Solving word problems using linear systems of two equations in two unknowns
in this site.


Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


What you ask cannot be done. You have two equations and three variables, namely X, x, and y. X and x are not now, never have been, and never will be the same thing.

However, going on the assumption that you were just being sloppy and actually meant:





Solve the first equation for :



Substitute the RHS expression in place of in the second equation and then solve for



... and then solve for . Once you know , substitute that value back into either original equation and solve for .

John

My calculator said it, I believe it, that settles it