You can add 4x to 8x because 4x is 4 x’sand 8x is 8x’s,
which is 4x’s + 8x’s to get 12 x’s or 12x.
But why can't you add 4x² + 2x? I don't understand why you can't
add a squared variable to the same letter that isn't squared.
It’s similar to counting animals in a pasture.
When taking inventory, you can combine two pigs (2p)
with three pigs (3p) and get 5 pigs (5p).
Also, you can combine four brown horses (4hbr) with three brown horses (3hbr) and get 7 brown horses (7hbr)
.......however you cannot combine a black horse (hbl) with a brown horse (hbr).
Just like you cannot combine 2 terms that have different exponents such as 4x2and 2x.
See more combining like terms examples here
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