A × B × C × D × E × F = 7 × 1 0 7
Determine the number of ordered solutions for integers A , B , C , D , E , F such that they satisfy the equation above.
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After you get to 3763584, you can also finish as follows: Choose the signs of A , B , … , E arbitrarily. Then the sign of F is uniquely determined, so you multiply 3763584 by 2 5 .
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OH NICE! Never thought of "Forcing F to be uniquely determined".
By this , we can prove that , ( n 0 ) + ( n 2 ) + ( n 4 ) + . . . . + ( n n ) ( w h e n n = e v e n ) is equal to ( n 0 ) + ( n 2 ) + ( n 4 ) + . . . . + ( n n − 1 ) ( w h e n n = o d d ) is equal to 2 n − 1
Very nice.Even I did the same way
did the same way...
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Even i was thinking of the exact same way but i was a bit scared,so:P:P:P
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I was scare too while submitting the answer but it was correct.... :)
Did you mean 6 negative integers for case 4?
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The factorization of 7 × 1 0 7 is simply 2 7 × 5 7 × 7 .
Suppose for now we restrict the search for positive integer solutions only.
For non-negative integers x i , y i , z i , let A = 2 x 1 ⋅ 5 y 1 ⋅ 7 z 1 , B = 2 x 2 ⋅ 5 y 2 ⋅ 7 z 2 , … , F = 2 x 6 ⋅ 5 y 6 ⋅ 7 z 6 .
Then their product is 2 7 × 5 7 × 7 1 = 2 ∑ j = 1 6 x j × 5 ∑ j = 1 6 x j × 7 ∑ j = 1 6 x j .
⇒ j = 1 ∑ 6 x j = 7 , j = 1 ∑ 6 y j = 7 , j = 1 ∑ 6 z j = 1 .
By Stars and Bars, we have ( 6 − 1 7 + 6 − 1 ) = ( 5 1 2 ) ordered solution for < x i > and < y i > , and ( 6 − 1 1 + 6 − 1 ) = 6 ordered solution for < z i > .
Multiplying them together gives a total of ( 5 1 2 ) 2 × 6 = 3 7 6 3 5 8 4 ordered solution for positive integers A to F .
If we drop the constraint for positive integers, then we could have:
Case 1 : 6 Positive integers
Case 2 : 4 positive integers, 2 negative integers
Case 3 : 2 positive integers, 4 negative integers
Case 4 : 6 Negative integers
Combining all these cases together yields a total of
3 7 6 3 5 8 4 × [ ( 0 6 ) + ( 2 6 ) + ( 4 6 ) + ( 6 6 ) ] = 1 2 0 4 3 4 6 8 8 ordered solutions.