How many terms will there be in your answer when you multiply and simplify (x+y)^3 ?

There will be four term.

This type of expansion follows Pascal's Triangle for its coefficients.

So the square expansion has coefficients 1 - 2 - 1 three terms

The cubed will be 1 - 3 - 3 - 1 four terms

The fourth power will be 1 - 4 - 6 - 4 - 1 five terms

And so on.

OK?

In general, the expansion of (x+y)^n has (n+1) terms.

In this case n=3, so there are 4 terms