HELP with subtraction?

Question

solve system by subtraction.?
5x-2y=-5
Y-5x=3
how do you do this problem?
or
8x-4y=16
y=2x-4
Im stumped

Answer 1

First rearrange the equations, so the x and y's line up.
5x - 2y = -5
-5x + y = 3
Add the two equations
-y = -2
y = 2
Now go back to one of the equations, replace y with 2 and solve for x.
5x - 2(2) = -5
5x - 4 = -5
Add 4 to each side
5x = -1
Divide both sides by 5
x = -1/5
Answer: (-1/5, 2)

The second question is easier to solve by substitution.
Replace y with 2x-4 in the first equation
8x - 4(2x-4) = 16
8x - 8x + 16 = 16
16 = 16
This equation is true, so that means there are infinitely many solutions of the form (x, 2x-4), where x is any real number.

Answer 2

First one:
you just add them together:
5x-2y = -5
-5x+y = 3
---------------
0x - y = -2

y = 2 substitute back into one of original eq:
x = -1/5

Second one (rearrange second eq):
8x - 4y = 16
2x - y = 4 ---> multiply both sides by 4 to get 8x - 4y = 16

These two equations are identical so you can not solve them for x and y. If you were to subtract them you would get 0x + 0y = 0.

Answer 3

5x-2y=-5 ---equation 1
y-5x=3 ---eaquation 2

using equation 2,
y-5x=3
y=3+5x ---equation 3

put equation 3 into equation 1
5x-2(3+5x)=-5
5x-6-10x=-5
-5x=-5+6
-5x=1
x=-1/5

Answer 4

this is TERRIBLY easy. you multiply the 2nd equation of the top problem by -5 and multiply the 2nd equation (2nd problem) by -4. then bring the y to the other side and solve.