substitution?

Question

soo how dus dis work?
its confusing

2x+5y=7
x+4y=2

help me please

Answer 1

OK - using substitution

Let's look at the second equation

x+4y = 2 ; subtract 4y from both sides
x = 2-4y ; COOL - we have x in terms of y, now substitute in the first equation!

2(2-4y) + 5y = 7 ; notice all y's now
4 - 8y + 5y = 7
-8y + 5y = 3
-3y = 3
y = -1

Now that you have y, substitute in back in the first equation

2x + 5(-1) = 7
2x -5 = 7
2x = 12
x = 6 .

x =6, y = -1.

Do final check in second equation
6 + 4(-1) = 2 ??
6 - 4 = 2 ??
2 = 2 YES!!!

Hope that helps.

Answer 2

From the 2nd equation we know that x = 2- 4y.
So we can substitute 2-4y for x in equation 1 getting
2(4-y) + 5y = 7
8 -2y +5y = 7
3y = -1
y=-1/3
Now stick y= -13 in 2nd equation and find x

Answer 3

1) multiply the second equation by -2, so that you can sum the equations and eliminate the x.

2x + 5y = 7
-2x -8y = -4
------------------ +
-3y = 3
y = -1

2) substitute the value of y to the either equation to find x. e.g. use the first equation:
2x + 5 * (-1) = 7
2x -5 = 7
2x = 12
x = 6

Answer 4

x+4y=2
x=2-4y
2(2-4y)+5y=7
4-8y+5y=7
-3y=-3
y=-1

x+4y=2
x+4(-1)=2
x-4=2
x=6

ANSWER
y=-1
x=6