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An equation with infinite solutions has a solution of x=x. You can plug in any x-value and it will equal x, so there are infinitely many solutions.
ANSWER A
10x-10=-10x+10
We add 10 to both sides.
10x=-10x+20
We add 10x to both sides.
20x=20
We divide both sides by 20.
x=1
We have a solution of 1, so this is not an equation with infinitely many solutions.
Answer B
-10x-10=-10x+10
We add 10 to both sides.
-10x=-10x+20
We add 10 x to both sides.
0=20
This has no solutions because the x is gone, so there cannot be a solution.
Answer C
-10x-10=-10x-10
We add 10 to both sides.
-10x=-10x
We divide both sides by -10.
x=x
This has infinitely many solutions.
Answer D
10x-10= -10x-10
We add 10x to both sides.
20x-10=-10
We add 20 to both sides.
20x=0
We divide both sides by 20.
x=0
There is a single solution here, not infinitely many.
Therefore, the answer is C. -10x-10=-10x-10.
Have a wonderful day! :D