To determine if three side lengths \( a \), \( b \), and \( c \) can form a triangle, they must satisfy the triangle inequalities. The first condition you provided is \( a < b + c \).
The other triangle inequalities that must be satisfied are:
- \( b < a + c \)
- \( c < a + b \)
From the choices you presented, we can analyze them one by one:
- \( a > b - c \): This does not directly correspond to a triangle inequality.
- \( b > a - c \): Again, this does not correspond to a triangle inequality.
- \( a < b - c \): This does not satisfy any triangle inequality as it's not valid.
- \( a > c - b \): This resembles a triangle inequality and can be interpreted as \( a + b > c \) (rearranging gives \( a > c - b \)).
Among these options, the valid second condition to use in conjunction with \( a < b + c \) is:
\( a > c - b \)
It reflects a valid triangle inequality condition where the sum of two sides should be greater than the third when rearranging terms.