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If k2 - 1 is divisible by 8, then K is:

Solution

✅ Correct Option: 4

Let me solve this:

If k2−1k^2 - 1 is divisible by 8, then:

k2−1=8mk^2 - 1 = 8m for some integer mm

k2=8m+1k^2 = 8m + 1

Since k2=(k+1)(k−1)+1k^2 = (k+1)(k-1) + 1, we can write:

(k+1)(k−1)(k+1)(k-1) must be divisible by 8

For consecutive integers (k+1)(k+1) and (k−1)(k-1):

  • If kk is even, one number is odd and other is odd
    • If kk is odd, one number is even and other is even

For their product to be divisible by 8, kk must be odd (so both (k+1)(k+1) and (k−1)(k-1) are even)

Therefore, kk must be an odd integer.

Alternatively, you can just put your own values for k according to the options and find out.

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