If 6 + 1 2 3 1 0 2 9 + 1 3 1 0 2 9 + n is an integer, then find the lowest possible value of n ( where n is a whole number ).
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2 3 = 7 k + 2 This implies that 2 3 × 2 3 × 2 3 = 7 y + 1 ( using modular arithmetic) This implies that 2 3 1 0 2 9 = 7 m + 1 Similarly, 1 3 1 0 2 9 = 7 n + 6 Therefore 2 3 1 0 2 9 + 1 3 1 0 2 9 = 7 k Thus n=0 & n=7
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We have to work mod 7 , since the denominator is 7. Hence,
2 3 1 0 2 9 + 1 3 1 0 2 9 + n ≡ 0 (mod 7)
Now, 2 3 1 0 2 9 ≡ 2 1 0 2 9 (mod 7)
Also, 2 3 ≡ 1 (mod 7) ⇒ ( 2 3 ) 3 4 3 ≡ 1 3 4 3 ≡ 1 (mod 7)
Along similar lines, 1 3 1 0 2 9 ≡ ( − 1 ) 1 0 2 9 ≡ − 1 (mod 7)
Hence, 2 3 1 0 2 9 + 1 3 1 0 2 9 + n ≡ 0 ⇔ 1 − 1 + n ≡ 0 (mod 7)
The lowest possible whole number is 0