Step 1: Understand the concept of straight-line depreciation. It is a method used to allocate the cost of an asset evenly over its useful life. The formula calculates the annual depreciation expense based on the asset's cost, salvage value, and useful life.
Step 2: Identify the components of the formula. The 'Cost' refers to the purchase price of the asset, 'Salvage Value' is the estimated residual value of the asset at the end of its useful life, and 'Useful Life' is the expected duration the asset will be used.
Step 3: Analyze the given formulas. The correct formula for annual straight-line depreciation is: \( \text{(Cost} - \text{Salvage Value)} \div \text{Useful Life} \). This formula subtracts the salvage value from the cost to determine the depreciable amount and divides it by the useful life to calculate the annual depreciation expense.
Step 4: Compare the other options provided. \( \text{Cost} \times \text{Depreciation Rate} \) is used for declining balance depreciation, \( \text{Cost} \div \text{Useful Life} \) ignores salvage value, and \( \text{(Cost} + \text{Salvage Value)} \div \text{Useful Life} \) incorrectly adds salvage value instead of subtracting it.
Step 5: Conclude that the correct formula for annual straight-line depreciation is \( \text{(Cost} - \text{Salvage Value)} \div \text{Useful Life} \), as it properly accounts for the depreciable amount and allocates it evenly over the asset's useful life.