183k views
4 votes
Solve by the elimination method.
8x−y=9
x+4y=30


User Spoida
by
8.3k points

1 Answer

2 votes

Answer:

x=2

y=7

Explanation:

if you look at both equations, you can see that instantly adding or subtracting them would not be a smart idea, therefore we should make one variable same absolute value on both equations. In this case, we sill try to keep the x, therefore we would try to get rid of y in both equations, so lets make y coefficient a 4

As we see in the second equation, y coefficient is already a 4 therefore we do not need to do anything there.

However if we look at the first equation, absolute value of y is 1, therefore we need to multiply both sides of first equation by 4, that would give us 4(8x-y)=4(9), which would give us 32x-4y=36.

Now we successfully have same absolute values of y in both equations, to determine whether or not subtract or add these equations, we need to determine which one would eliminate the y, we need to determine whether or not y is positive or negative, in the first equation y is negative, on the second equation, however, the y is positive. therefore we should add these equations in order to get rid of y.

32x-4y=36

+

x+4y=30

This would give us 33x=66

From now on we can easily determine the value of x by dividing both sides by 33 which would give us x=2

Now that we know the x value, we can use this value to determine the y value, if we look at second equation (x+4y=30) we can replace x with 2

New equation would be 2+4y=30

minus 2 on both sides would give us 4y=28

From her, we can divide both sides by 4 which would give us y=7

Hope it helped, let me know If you have any questions, I would happy to answer.

User Marko Stojkovic
by
8.6k points