Which expression can be substituted for y in the top equation of the system 3x+4y=-1 x-y=3 to solve the system by substitution ?

Answer 1

Assuming that top equation is 3x + 4y = -1, then you can solve the equation x-y =3 for y and substitute this expression into the Top Equation.

x - y = 3

You can first subtract x from both sides of the equation to get:

x - y - x = 3 - x

11/then -y = 3 -x

Next divide both sides of the quation by -1:

-y /-1 = (3-x )/-1

Then y = -3 + x OR y = x-3

Substitute x-3 for y into the TOP EQUATION:

3x + 4(x -3) = -1

Now use inverse operations, combining like terms, and the distributive property to solev:

3x + 4x - 12 = -1

7x - 12 = -1

7x -12 + 12 = -1 + 12

7x = 11

7x/7 = 11/7

x = 11/7

For y:

y = x -3

y = 11/7 -3

y = 11/7 -21/7

y =-10/7

You can check your solution by "trying the numbers" in either equation:

x - y = 3

11/7 - (-10/7) = 21/7 or 3