Answer:
Part A:
[tex]x\in \mathbb{R}[/tex] ([tex]x[/tex] is equal to all real numbers)
Part B:
[tex]5+(-4)-12=-4-7,\\-11=-11\:\checkmark,\\\\5+0-12=0-7,\\-7=-7\:\checkmark,\\\\5+5-12=5-7,\\-2=-2\:\checkmark[/tex]
Step-by-step explanation:
Part A:
Given [tex]5+x-12=x-7[/tex], combine like terms:
[tex]x-7=x-7[/tex]
Add 7 to both sides:
[tex]x=x[/tex]
Since this is merely a true statement for all real numbers (reflexive property), this equation is true for any real value of [tex]x[/tex].
Therefore,
[tex]x\in \mathbb{R}[/tex] ([tex]x[/tex] is equal to all real numbers).
Part B:
Using arbitrary values [tex]x=-4, x=0, x=5[/tex] as requested in part B, verify:
[tex]5+(-4)-12=-4-7,\\-11=-11\:\checkmark,\\\\5+0-12=0-7,\\-7=-7\:\checkmark,\\\\5+5-12=5-7,\\-2=-2\:\checkmark[/tex]