Robin thinks that 4x+5x2 is the same as 9x3. Which statement shows that it is NOT the same?

You can substitute numbers in for x to prove it is not true:

4x+5x² and 9x³

Using 3 for x,

4 (3) + 5 (3²) and 9 (3³)

12+5 (9) and 9 (27)

12+45 and 243

57 and 243

These are obviously not the same.

Algebraically speaking, they do not go together because x³ is multiplying; we did not multiply x² and x, we added them.