Explanation:
if you brought this in here correctly, oh, it is a real mystery !
common sense ! we need common sense !
what can I add to e.g. 15 to still keep the 15 ?
this works with any other number as well.
e.g. 1
I have 1.
how much can I add to 1 to still have 1 afterwards ?
1+? = 1
? = 0
right. there is no other solution, as there are also no miracles in math.
whatever is added, is then added. to remain unchanged we can only add 0.
so,
15 + something = 15 can only be true, if that something is 0.
something = |3x|
that means the absolute value of 3x, which will always be +3x even for negative x.
but it does not matter.
|3x| = 0 (has to be 0 to make the main statement true).
therefore, 3x = 0
therefore, x = 0.
so, they're is only one dot (a filled dot) at precisely 0 in the graph that makes this a true statement.