SOLUTION: Solve the systems of equations by substitution: 3x+y= -8 4x+3y=7 I have been working with different types of equations all night on homework and I'm not sure if I just don't un

Algebra ->  College  -> Linear Algebra -> SOLUTION: Solve the systems of equations by substitution: 3x+y= -8 4x+3y=7 I have been working with different types of equations all night on homework and I'm not sure if I just don't un      Log On


   

Question 997949: Solve the systems of equations by substitution:
3x+y= -8
4x+3y=7
I have been working with different types of equations all night on homework and I'm not sure if I just don't understand it or if I'm doing something small wrong I just can't seem to get the correct answer.
Found 2 solutions by MathLover1, addingup:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!
Solve the systems of equations by substitution:
3x%2By=+-8....eq.1
4x%2B3y=7....eq.2
-------------------------
start with 3x%2By=+-8....eq.1, solve for y
y=-3x+-8...eq.1a...now, substitute it in eq.2
4x%2B3%28-3x+-8%29=7....eq.2....solve for x
4x-9x+-24=7
-5x+-24=7
-7+-24=5x
+-31=5x
x=+-31%2F5
highlight%28x=+-6.2%29....now, go back to y=-3x+-8...eq.1a,substitute -6.2 for x and find y
y=-3%28-6.2%29+-8
y=18.6+-8
highlight%28y=10.6%29+







Answer by addingup(3677) About Me  (Show Source):
You can put this solution on YOUR website!
3x+y= -8
4x+3y= 7
We can begin with either one of the equations, but since we have a "y" all by itself in the first equation, let's start with the first equation:
3x+y= -8
y= -8-3x
Now we plug this value for y into the second equation (Warning: If we substitute into the same equation we would get a true, but useless, statement. Always substitute into the other equation)
4x+3(-8-3x)= 7 Now we can solve for x:
4x+-24-9x= 7
= 4x-24-9x= 7 Add 24 on both sides and add x on left:
-5x= 31
x= 31/-5= -6 1/5 And y?:
y= -8-3(-6 1/5)
y= -8+18 3/5
y= 26 3/5
J