x 1 , x 2 , x 3 , . . . . . . . . . , x 1 0 are integers , none of which are divisible by 3 . The remainder when x 1 2 + x 2 2 + x 3 2 + . . . . . . . + x 1 0 2 is divided by 3 is
This problem is a part of the sets - 3's & 4's & " N " for number theory
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Given that none of x 1 , x 2 , x 3 , … , x 1 0 are divisible by 3, we know that for each i = 1 , 2 , 3 , … , 1 0 , x i ≡ 0 ( m o d 3 ) . Then either x i ≡ 1 ( m o d 3 ) or x i ≡ 2 ( m o d 3 ) . If x i ≡ 1 ( m o d 3 ) , then x i 2 ≡ 1 ( m o d 3 ) . If instead x i ≡ 2 ( m o d 3 ) , then x i 2 ≡ 4 ≡ 1 ( m o d 3 ) . In either case, x i 2 ≡ 1 ( m o d 3 ) , so x 1 2 + x 2 2 + x 3 2 + … + x 1 0 2 ≡ 1 0 ≡ 1 ( m o d 3 ) . Thus the remainder is 1.
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x 1 , x 2 , x 3 , . . . . . . . . . , x 1 0 these integers are in 3 k + 1 or 3 k + 2 form.
( 3 k + 1 ) 2 = 3 m + 1
( 3 k + 2 ) 2 = 3 n + 1
Thus the all ten integers are in 3 k + 1 form
Their sum leaves remainder of 1 0 ∗ 1 getting divided by 3.
The answer is 1