1. **State the problem:** Simplify the expression $R = 2 - 5 + r_1 r_2 r_6$. 2. **Apply arithmetic operations:** First, simplify the constant terms $2 - 5$. 3. Calculate $2 - 5 = -3$. 4. Substitute back into the expression: $$R = -3 + r_1 r_2 r_6$$. 5. **Final simplified form:** The expression cannot be simplified further without values for $r_1$, $r_2$, and $r_6$. Therefore, the simplified expression is $$R = -3 + r_1 r_2 r_6$$.