To express $(x + 3)^2$ as a trinomial, you need to expand it using the formula for the square of a binomial, which is:

$(a + b)^2 = a^2 + 2ab + b^2$

Here, $a = x$ and $b = 3$. Let's apply this:

$(x + 3)^2 = x^2 + 2(x)(3) + 3^2$

Simplifying:

$x^2 + 6x + 9$

So, the trinomial form of $(x + 3)^2$ is:

$x^2 + 6x + 9$

Would you like further details or have any other questions?

Here are 5 related questions for practice:

1. What is the result of $(x - 4)^2$?
2. How would you expand $(2x + 5)^2$?
3. Can you expand $(x + 7)^2$ using the same method?
4. What is the simplified form of $(3x + 2)^2$?
5. How does the middle term change when squaring a binomial with a negative second term?

Tip: Always remember the middle term comes from doubling the product of the two terms in the binomial!