Ask Singapore Homework?
Upload a photo of a Singapore homework and someone will email you the solution for free.
Question
secondary 3 | A Maths
One Answer Below
Anyone can contribute an answer, even non-tutors.
I don't understand how to tackle this "Challenge Yourself" question from the Amath 360 TB 3A 2nd Ed.
I'm hoping someone can give me an explanation and enlighting me how to go about deriving and proving the explanation. Thanks!
See 1 Answer
49 = 1 + 48 (note that 48 is divisible by 8)
So 49^15 = (1 + 48)^15
= 1^15 + (15choose1)(1^14)(48) + (15choose2)(1^13)(48²) + ... + (15choose13)(1²)(48^13) + (15choose14)(1)(48^14) + 48^15
Every term in the expansion has a multiple of 48 as a factor, except 1^15. So the sum of all those terms except 1^15 are also divisible by 48 (which in turn implies they are divisible by 8 also).
1^15 = 1 so subtracting 1 from 49^15 takes it away. This would make the remaining expression divisible by 8.
We must actually also mention that the other terms in the expansion, including nCr, are also integers.
It is understood that for the binomial theorem, the combination (n r) will only be an positive integer since n and r are positive integers and r ≤ n. This is clearly shown in the Pascal's triangle
We do not have to be concerned about the non-integer n and r here (that is under the topic of gamma function)