answer please...........
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= 1²+2²+3²+4²+5²+6²+7²+8²+9²+...+39² - 1²-2²-3²-4²-6²-8²-10²-...-38²
we know formula = n(n+1)(2n+1)/6
= (1²+2²+3²+4²+...+39²) - 2²(1+2²+3²+4²+...+19²) - 1²-3²
= 39*(40)*(79)/6 - 4*(19)*(20)*(39)/6 - 1 - 9
= 13*20*79 - 4*19*10*13 - 10
= 20,540 - 9,880 - 10
= 10,650
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