To solve for the length of \( LS \), we can use the formula for the length of an arc in a spherical triangle. In this situation, we will utilize the spherical law of cosines.
We have:
- \( YS \) = 6.3 km
- \( YL \) = 15.4 km
- \( S \) is the apex (or vertex) of triangle \( YLS \).
Let us denote:
- \( a = YL \) (length opposite to side \( LS \))
- \( b = YS \) (length opposite to side \( LY \))
- \( c = LS \) (the side we want to find)
From the information provided, we can assume we are dealing with spherical geometry where the variable \( s \) (the apex) will relate to these lengths.
Using the spherical law of cosines for a triangle:
\[ \cos(c) = \cos(a) \cos(b) + \sin(a) \sin(b) \cos(S) \]
In this case we do not have an angle \( S \), so we cannot directly apply the formula without more context or further information.
To derive \( LS \) specifically, we might need a specific relationship or known angle at vertex S (apex). However, if we assume \( a \) and \( b \) are legs of a triangle rather than taking angle \( S \) into account:
In a planar triangle setup, we might consider that:
\[ LS^2 = YS^2 + YL^2 - 2 \cdot YS \cdot YL \cdot \cos(S) \]
Without \( S \), we cannot exactly calculate it. Could you please provide either the angle at S or specify how you wish to approach this?
Based on the data, the calculation to find \( LS \) requires some assumptions or further clarification on how to calculate the third side \( LS \). Please confirm if there are any further data or assumptions!