Question

x-2x=1

Answer 1

Just reduce -2x from x from this way :
-2x+x=1
-x=1
x=-1
Got it ?

Answer 2

x-2x=1
-x=1
x=-1
true ??

Answer 3

Yes !

Answer 4

x - 2x = 1 (combine like terms)
-x = 1 (multiply by -1 to make x positive)
x = -1