4. Solve the following system of equations by

a) Graphing

Solve each equation for y. For the first one,

first, transpose the x term to the other side of the equation.

We do the same thing with the other equation.

but here we also have a coefficient to remove.

Divide both sides by -2.

Make up a table of x's and y' for each equation, and graph them

both.

and we see that the solution is x = -1 and y = 3.

Check

top

if we substitute these numbers into the first equation, we get

2(-1)+ (3) = 1

-2 + 3 = 1

which checks.

In the second equation we get

(-1) - 2(3) = -7

-1 - 6 = -7

so they check in both equations

b) Substitution.

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Solve one of the equations for one of the unknowns. In this

case, it would be best to solve the second equation for x.

Substitute this solution into the other equation

This gives us an equation with only one unknown. Solve this

equation. First, remove parentheses.

Combine the y terms on the left and transpose the -14 to the

other side.

or

Divide both sides by 5.

To find x, substitute this solution into the equation where we

had solved for x as a function of y,

and get

or

which is the same solution as we got before.

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Multiply the equations by suitable numbers so that the

coefficients of the y terms match up. In this case we could simply

multiply the top equation by 2.

or

To solve for y, substitute this solution into either of the original

equations and solve for y. The best equation would be the first one

or

so all we have to do to solve for y is to add 2 to both sides.