lo g ( a + b + c ) = lo g ( a ) + lo g ( b ) + lo g ( c )
a < b < c are positive integers that satisfy the equation above. Find a 2 b 3 c 4 .
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A perfect number isn't that whose factors multiply to the number, only the sum matters, 28 is also perfect number, but 1 ⋅ 2 ⋅ 4 ⋅ 7 ⋅ 1 4 = 2 8
lo g ( a + b + c ) lo g ( a + b + c ) ⟹ a + b + c = lo g a + lo g b + lo g c = lo g ( a b c ) = a b c
This implies that a = 1 , b = 2 , and c = 3 , and a 2 b 3 c 4 = 1 × 8 × 8 1 = 6 4 8 .
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Given that a , b and c are positive integers and a < b < c ,
lo g ( a + b + c ) lo g ( a + b + c ) ⟹ a + b + c suppose a ≥ 2 , then b ≥ 3 a + b + c ⟹ b + c min. of RHS 1 + b + c ⟹ c ( b − 1 ) a 2 b 3 c 4 = lo g ( a ) + lo g ( b ) + lo g ( c ) = lo g ( a ⋅ b ⋅ c ) = a ⋅ b ⋅ c = a ⋅ b ⋅ c = a ( b c − 1 ) = 2 ( 3 c − 1 ) = 6 c − 2 = c + ( 5 c − 2 ) > LHS as b < 5 c − 2 for c ≥ 3 ⟹ contradiction ⟹ a = 1 = b ⋅ c = b + 1 ⟹ c = b − 1 b + 1 ⟹ b = 2 ⟹ 1 + 2 + c = 2 c ⟹ c = 3 = 1 2 2 3 3 4 = 1 ⋅ 8 ⋅ 8 1 = 6 4 8