To get the answer of -2.5 from the expression 1/2cos0-3, we need to follow the order of operations.
Here is the step-by-step solution:
1. First, we need to evaluate the cosine of 0 degrees. The cosine of 0 is 1. So, the expression becomes:
1/2 * 1 - 3
2. Next, we need to simplify the expression by multiplying 1/2 with 1. So, we get:
1/2 - 3
3. Now, we need to subtract 3 from 1/2. So, we get:
-2.5
*Therefore, the final answer is -2.5.