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But why are we using x^4k, if we use x^2k, answer would be NOT SUFFICIENT.
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But why are we using x^4k, if we use x^2k, answer would be NOT SUFFICIENT.

But 40 can be written as 4*10 = 4k
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I understand but my doubt is why can't it be written as 2*20, what is the question asked x^80? Would we still write 8*10 or 4*20?
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I understand but my doubt is why can't it be written as 2*20, what is the question asked x^80? Would we still write 8*10 or 4*20?

2,4,8,16,32 => last digits 2,4,8,6,2 => last digit is 6 and is repeated after 2^4k
4,16,64,216 => last digits 4,6,4,6 => last digit is 6 and is repeated after 4^4k
Similarly for 6 => last digit is 6 and is repeated after 6^4k
Similarly for 8 => last digit is 6 and is repeated after 8^4k
But for 0 => last digit is 0 and NOT 6 and is repeated after 0^4k

To find last digit, we have to make sure x is even but last digit of x is NOT 0, in all other cases x^4k will have last digit as 6.
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Thank You, I made a silly mistake in calculation.
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