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How do I solve this, and how do I know if I need to add or subtract at the beginning

How do I solve this, and how do I know if I need to add or subtract at the beginning-example-1
User NIA
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1 Answer

9 votes
9 votes

Let's solve the system of equations using elimination:

4x + 5y = 14

-4x -2y = -8

First, we need to get rid of one variable.

Sometimes we multiply them by some factors to have the same number on one variable, but in this case, we can subtract the x variable

4x +5y =14

-4x-2y = -8

----------------------

4x-4x =0, 5y -2y = 3y and 14-8=6

------------------------------

0+3y = 6

Solve the equation for y

Divide by 3 into both sides

3y/3 = 6/3

y = 2

Then, replace this variable on one equation, whichever you want:

4x + 5y = 14

4x +5(2) = 14

4x +10 = 14

and solve the equation for x

4x +10 = 14

Subtract 10 on both sides

4x +10-10 = 14-10

4x = 4

Divide by 4 into both sides

4x/4 = 4/4

x = 1

You can replace both variables to confirm the results:

4x +5y =14

4(1) +5(2) = 14

4 +10 = 14

14 = 14

---------------------------------

-4x -2y = -8

-4(1) -2(2) = -8

-4-4 = -8

-8 = -8

The result is correct, so my ordered pair is (x,y) = (1,2)

User Bart N
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