SubArea: CombinatoricsLevel: CProject ID: 1003024701Source Problem: 2010007602Accepted: 1Clonable: 1Easy: 0What is the coefficient at \( x^7 \) in the expansion of \( (1-3x)^9 \)?\( -78\:732 \)\( 59\:049 \)\( -59\:049 \)\( 78\:732 \)
