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The sum of the products of the ten numbers `+-1,+-2,+-3,+-4,+-5` taking two at a time is: |
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Answer» we know, `(a+b)^2 = a^2 + b^2 + 2ab` `(a+b+c)^2 = a^2 + b^2 +c^2 + 2(ab+bc+ca)` numbers given `1,2,3,4,5,-1,-2,-3,-4,-5` `(1+2+3+4+5-1-2-3-4-5)^2 = 1^2 + 2^2 + 3^2 + 4^2 + 5^2 + 1^2 + 2^2 + 3^2 + 4^2 + 5^2 + 2(s)` `0 = 2(1^2 + 2^2 + 3^2 + 4^2 + 5^2) + 2(s) ` `s = -(1^2 + 2^2 + 3^2 + 4^2 + 5^2)` `s = -(5 xx 6 xx 11)/6` `= - 55` option b is correct answer |
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