Find the number of triples (a, b, c) of positive integers, such that 1 <= a, b, c <= 100 and a^2 + b^2 + c^2 = + ab + ac + bc = 81.
a^2 + b^2 + c^2 = 81
Let's list the squares under 81.
1, 4, 9, 16, 25, 36, 49, 64
Now the ones that add up to 81.
1, 16, 64 (1, 4, 8)
16, 16, 49 (4, 4, 7)
9, 36, 36 (3, 6, 6)
Now let's check for the second criteria.
ab + ac + bc = 81
1*4 + 4*4 + 4*1 != 81
4*4 + 4*7 + 4*7 != 81
3*6 + 6*6 + 3*6 != 81
I found 0 triples, but there are probably some more.
Sorry I couldn't help more.
=^._.^=