Two electronics technicians are looking at the testing instrument in the figure above. Technician A says that this instrument is
used to measure electrical signals in a circuit and display them as waveforms on a screen. Technician B says that this instrument is called a signal generator. Which of the following statements is correct?
A. Only Technician A is correct.
B. Neither of the two technicians is correct.
C. Both Technician A and Technician B are correct.
D. Both Technician B is correct
A. Only Technician A is correct.
B. Neither of the two technicians is correct.
C. Both Technician A and Technician B are correct.
D. Both Technician B is correct
1 answer:
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The recursive function would work like this: the n-th odd number is 2n-1. With each iteration, we return the sum of 2n-1 and the sum of the first n-1 odd numbers. The break case is when we have the sum of the first odd number, which is 1, and we return 1.
int recursiveOddSum(int n) {
if(2n-1==1) return 1;
return (2n-1) + recursiveOddSum(n-1);
}
To prove the correctness of this algorithm by induction, we start from the base case as usual:
by definition of the break case, and 1 is indeed the sum of the first odd number (it is a degenerate sum of only one term).
Now we can assume that returns indeed the sum of the first n-1 odd numbers, and we have to proof that
returns the sum of the first n odd numbers. By the recursive logic, we have
and by induction, is the sum of the first n-1 odd numbers, and 2n-1 is the n-th odd number. So,
is the sum of the first n odd numbers, as required: