Higher order functions in Python using reduce technique
If a homework problem starts with the words "Show that", I would expect the answer to contain a proof (or at least an argument), not just an implementation.
You've misunderstood the problem statement. It says that start "specifies what value to use to start the accumulation", but in your implementation, start is the index of the first item in the sequence to contribute to the accumulation. Both of the test cases have start=1 and f(1)=1 so they are incapable of detecting your mistake.
Your implementations of summation_using_accumulate and product_using_accumulate do not actually use accumulate!