We can compute: For each (S), (r = (-2S) \mod 9 = (-2S + 18m) \mod 9). Better: ( -2S \equiv 7S \pmod9) because -2 ≡ 7 mod 9. So (C \equiv 7S \pmod9).
A(0,0), B(2,0), C(2,2), D(0,2). E = midpoint of AB = (1,0). F = midpoint of BC = (2,1). Mathcounts National Sprint Round Problems And Solutions
Problem 2: A sequence of numbers is defined recursively as: $a_n = 2a_n-1 + 3$. If $a_1 = 5$, what is $a_4$? We can compute: For each (S), (r =