1²+2²+3²+4²+.+19²+20²
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![1²+2²+3²+4²+.+19²+20²](/uploads/image/z/588991-31-1.jpg?t=1%26%23178%3B%2B2%26%23178%3B%2B3%26%23178%3B%2B4%26%23178%3B%2B.%2B19%26%23178%3B%2B20%26%23178%3B)
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1²+2²+3²+4²+.+19²+20²
1²+2²+3²+4²+.+19²+20²
1²+2²+3²+4²+.+19²+20²
平方和公式n(n+1)(2n+1)/6
n=20
1²+2²+3²+4²+.+19²+20²=20*(20+1)(40+1)/6=2870