algebra
posted by unowen
15 can be written as the difference between two positive perfect squares:
15=4²1²=161
Which of the following numbers cannot be written as the difference of two positive perfect squares?
16
17
18
19
20

PsyDAG
These are not differences.
17 = 4^2 + 1^2
16 = 2^2 * 2^2
20 = 4^2 + 2^2
18 = 3^2 + 3^2
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