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The greatest natural number by which the product of three consecutive even natural numbers is always divisible is:
16
48
24
96
48
Test the first few cases: for 2, 4, 6 the product is 48; for 4, 6, 8 the product is 192. The GCD of 48 and 192 is 48.
Three consecutive even natural numbers.
P=(2nтИТ2)├Ч(2n)├Ч(2n+2)=8n(nтИТ1)(n+1)=8(n3тИТn)
Test the first few cases: for 2, 4, 6 the product is 48; for 4, 6, 8 the product is 192. The GCD of 48 and 192 is 48.
Many students only consider the first set (2, 4, 6), resulting in 48, but failing to verify that 48 is indeed the greatest common divisor for all sequences.
Define the numbers
Let the three consecutive even natural numbers be 2nтИТ2, 2n, and 2n+2, where n is a natural number starting from 2.
2nтИТ2,2n,2n+2
Calculate the product
The product is P=(2nтИТ2)(2n)(2n+2)=23(nтИТ1)(n)(n+1)=8(n3тИТn).
P=8(nтИТ1)n(n+1)
Analyze divisibility
The expression (nтИТ1)n(n+1) is the product of three consecutive integers, which is always divisible by 3!=6. Therefore, P is divisible by 8├Ч6=48.
P=8├Ч6k=48k
B is correct because the product of any three consecutive even natural numbers is always a multiple of 48, and 48 is the greatest such number.
This concept of 'product of k consecutive integers is divisible by k!' is a fundamental property used in combinations and sequences.