To complete the formula for the surface area of a triangular prism, we can break it down into components. The total surface area \( S.A. \) is the sum of the areas of the triangular bases and the rectangular lateral faces.
Here's how you can complete the formula:
\[ S.A. = B + (S_1 + S_2 + S_3) \]
Where:
- \( B \) is the area of the two triangular bases (often represented as \( 2 \times \text{Area of base triangle} \)).
- \( S_1, S_2, S_3 \) are the areas of the three rectangular lateral faces.
So, the formula can also be expanded as:
\[ S.A. = 2B + (S_1 + S_2 + S_3) \]
But in the context you've provided, simply completing it as:
\[ S.A. = B + (S_1 + S_2 + S_3) \]
is sufficient.