1. **Problem Statement:** Given that SU is a midsegment of triangle $\triangle RTV$ and $RV = 10$, find the length of $SU$. 2. **Key Concept:** A midsegment in a triangle connects the midpoints of two sides and is parallel to the third side. The length of the midsegment is half the length of the side it is parallel to. 3. **Formula:** If $SU$ is the midsegment parallel to side $RV$, then: $$SU = \frac{1}{2} RV$$ 4. **Calculation:** Substitute $RV = 10$: $$SU = \frac{1}{2} \times 10 = 5$$ 5. **Answer:** The length of $SU$ is $5$.