At higher voltage, cost of transmission is decreased.

Explanation:
Higher voltage transmission has several advantages over lower voltage transmission. Let's discuss them in detail:

1. Reduced Current:
- When the voltage is increased, the current required for the same power transmission decreases.
- According to Ohm's Law (V = I × R), for the same power (P), if voltage (V) increases, the current (I) decreases.
- As a result, lower current reduces resistive losses in the transmission lines.

2. Reduced Resistive Losses:
- The resistive losses in a transmission line are given by the formula P_loss = I^2 × R, where I is the current and R is the resistance of the line.
- As discussed earlier, higher voltage transmission reduces the current, which in turn reduces the resistive losses.
- Lower resistive losses mean that a greater amount of power reaches its destination, resulting in increased efficiency.

3. Reduced Size of Conductors:
- As the current decreases with higher voltage transmission, it allows for the use of smaller conductors.
- Smaller conductors are cheaper and require less material, reducing the overall cost of transmission line construction.

4. Increased Efficiency:
- Higher voltage transmission reduces resistive losses and allows for the transmission of more power with the same amount of current.
- This increased efficiency means that less power is wasted during transmission, resulting in cost savings.

5. Improved Voltage Regulation:
- Higher voltage transmission helps to maintain voltage levels within acceptable limits.
- When power is transmitted over long distances, voltage drops occur due to resistive losses. With higher voltage, the initial voltage at the source is higher, compensating for the voltage drop, and ensuring that the desired voltage is maintained at the load end.

Conclusion:
Based on the above explanations, it is clear that at higher voltage, the cost of transmission is decreased. This is mainly due to the reduced current, lower resistive losses, reduced size of conductors, increased efficiency, and improved voltage regulation.