**Prismatic Bar Fixed at Both Ends**
A prismatic bar refers to a structural element that has a constant cross-section along its length. When a prismatic bar is fixed at both ends, it means that the supports at both ends do not allow any rotation or translation.

**Axial Load at a Distance 'a' from One Support**
In this scenario, an axial load is applied at a distance 'a' from one of the supports. This means that the load is not applied directly at the support but at a certain distance away from it.

**Reaction at the Supports**
The reaction at the supports can be determined by analyzing the equilibrium of forces acting on the prismatic bar. Since the bar is fixed at both ends, the reaction forces at the supports will be equal and opposite in direction.

**Equilibrium of Forces**
To determine the reaction at the supports, consider the equilibrium of forces in the horizontal and vertical directions.

1. Horizontal Equilibrium:
Since the bar is fixed at both ends, the horizontal reaction forces at the supports must be equal and opposite to balance the applied load. Therefore, the horizontal reaction forces at both supports will be zero.

2. Vertical Equilibrium:
To analyze the vertical equilibrium, consider the moments about one of the supports. The moment caused by the applied load can be calculated as the product of the load magnitude and the distance 'a'.

Summing up the moments about one of the supports, we have:
Reaction at the support * Distance = Applied Load * Distance

Therefore, the reaction at the support can be calculated as:
Reaction at the support = Applied Load / Distance

**Final Answer**
Based on the above analysis, the reaction at the supports will be:
(1) Pb/a b, Pa/a b