To determine how many triangles a pentagon can be divided into by drawing all diagonals from one vertex, we can use a formula for any polygon. The number of triangles formed is given by:

$\text{Number of triangles} = n - 2$

where $n$ is the number of sides of the polygon.

In this case, a pentagon has 5 sides ($n = 5$):

$\text{Number of triangles} = 5 - 2 = 3$

Thus, the correct answer is:

A. 3

Would you like more details or have any questions?

Here are 5 related questions for you to explore:

1. How many triangles can be formed from a vertex in a hexagon?
2. What is the relationship between the number of sides in a polygon and the number of diagonals?
3. How do you calculate the interior angle sum of a polygon?
4. How do you determine the number of diagonals in a polygon?
5. How many diagonals are there in a regular octagon?

Tip: For any $n$-sided polygon, the formula to find the number of triangles formed from one vertex is $n - 2$.