show that the square of any positive integer can't be of the form 5m+2 or 5m+3 where M is a whole number
Answers
Answer:
==> a = 5( 5q² + 8q + 3 ) + 1 . °• a = 5m + 1 . [ Where m = 5q² + 8q + 3 ] . → Therefore, square of any positive integer in cannot be of the form 5m + 2 or 5m + 3 .
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Given : square of any positive integer
To Find : show that the square of any positive integer can't be of the form 5m+2 or 5m+3
Solution:
with out losing generality any number can be of form
5k , 5k+1 , 5k+2 , 5k+3 , 5k+4
(5k)² = 25k² = 5(5k²) = 5m
(5k+1)² = 25k² + 10k + 1 = 5(5k² + 2k) + 1 = 5m+1
(5k+2)² = 25k² + 20k + 4 = 5(5k² + 4k) + 4 = 5m+4
(5k+3)² = 25k² +30k + 9 = 25k² +30k + 5 + 4 = 5(5k² + 6k + 1 ) + 4 = 5m+4
(5k+4)² = 25k² + 40k + 16 = 25k² +40k + 15 + 1 = 5(5k² + 8k+3) + 1 = 5m+1
5m , 5m+1 & 5m + 4 are the only
Hence 5m+2 or 5m+3 can't be of the form
QED
square of any positive integer can't be of the form 5m+2 or 5m+3
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