3x-4y=-4 x+3y=-10

Question

Elimination using multiplication. 

Answer 1

Daniel, what we want is to add our two equations and have one of the variables cancel out. 

 

The easiest way to do that is to multiply the 2nd by -3. This gives us -3x - 9y = 30.

 

Now we have

 3x - 4y = -4

-3x - 9y = 30

 

If we add the two together, 3x - 3x = 0. -4y - 9y = -13y. -4 + 30 = 26.  So, we have

-13y = 26

 

Dividing both sides by -13, y = -2.

 

You should know from here how to find x. Hope this helps!

Answer 2

3x - 4y = -4

 x + 3y = -10

 

Multiply the second equation by -3:  3x - 4y = -4

                                                              -3x - 9y = 30

 

Adding the equations, we get -13y = 26, so y = -2.

 

Substitute for y in either one of the given equations:  

 

3x - 4(-2) = -4

3x + 8 = -4

3x = -12

x = -4

 

SOLUTION:  x = -4 and y = -2