Question

Usebthe elimination method to solve the following system of equations
4x+y=13
5x-y=5​

Answer 1

x = -2, y = 21

Explanation:

Let 4x + y = 13 to be equation1 {eqn1}

and let 5x - y = 5 to be equation2 {eqn2}

Using elimination method, you would try to make sure a particular unknown has the same value in both equation 1 and 2. This would make it easy for you to subtract one equation from the other.

Notice how the value of y is the same in both equations. That's a good sign.

But the signs aren't the same. Meaning y in eqn1 has a value of +1, and y in eqn2 has a value of -1. We need to make them similar.

So, we multiply the value of y in eqn1 by all the terms in eqn2. And, do pretty much the same thing by multiplying the value of y in eqn2 by all the terms in eqn1.

You would have:

-1 * (4x + y = 13)

+1 * (5x - y = 5)

This would result in;

-4x - y = -13 (eqn3)

5x - y = 5 (eqn4)

So, just subtract eqn3 from 4

You would have;

(5x - -4x) + (-y -- y) = (-13 - 5)

9x + 0 = -18

x = -18/9 = -2

and to find y;

just substitute the value of x into any of the 4 equations. let's try equation 1

Therefore;

4(-2) + y = 13

-8 + y = 13

y = 13 + 8 = 21