Question

find all positive integers n such that n^4-1 is divisible by 5

Answer 1

Answer:

The first few terms of a sequence of positive integers divisible by 5 is given by

5,10,15,...

The above sequence has a first term equal to 5 and a common difference d=5. We need to know the rank of the term 1555. We use the formula for the nth term as follows

1555=a

1

+(n−1)d

Substitute a

1

and d by their values

1555=5+5(n−1)

Solve for n to obtain

n=311

Step-by-step explanation:

We now know that 1555 is the 311th term, we can use the formula for the sum as follows

S

311

=

2

311(5+1555)

=242580

Hope it will help you