SOLUTION: My daughter is supposed to solve this problem using substitution. I don't get it. The problem is: -7x-2y= -13 x-2y=11 Can you help me try to explain this to her?

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Question 256543: My daughter is supposed to solve this problem using substitution. I don't get it. The problem is:
-7x-2y= -13
x-2y=11
Can you help me try to explain this to her?
Found 2 solutions by Alan3354, ankor@dixie-net.com:
Answer by Alan3354(69443) (Show Source):
You can put this solution on YOUR website!
-7x-2y= -13
x-2y=11 --> x = 2y+11
-------------
Sub for x into the 1st eqn
-7(2y+11) - 2y = -13
-14y-77 - 2y = -13
-16y = 64
y = -4
---------
sub for y into either eqn
x-2y=11
x-2(-4) = 11
x+8 = 11
x = 3

Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website!
substitution. I don't get it. The problem is:
-7x - 2y = -13
x - 2y = 11
:
Choose one of the equation to use for substitution, the 2nd equation
x - 2y = 11
Add 2y to both sides
x = 2y + 11
:
Now we can substitute (2y+11) for x in the 1st equation, find y
-7x - 2y = -13
-7(2y+11) - 2y = -13
Multiply what's inside the brackets by -7
-14y - 77 - 2y = -13
add 77 to both sides
-14y - 2y = - 13 + 77
do the math
-16y = +64
The variable has to be positive, multiply both sides by -1
16y = -64
Divide both sides by 16
y =
y = -4
:
Solve for x in the 1st equation, substitute -4 for y in the 1st equation
:
-7x - 2y = -13
-7x - 2(-4) = -13
-7x + 8 = -13 Subtract from both sides
-7x = -13 - 8
-7x = -21
Multiply both sides by -1
7x = 21
x =
x = +3
:
:
Check solutions in the 2nd equaiton x-2y=11
3 - 2(-4) = 11
3 + 8 = 11; confirms our solutions