M(m-n)+2(m-n)=m2-mn+2m-2n
Ctg(2x) = 1/√3
2x = arcctg(1/√3) + πn, n∈Z
2x = π/3 + πn, n∈Z
x = π/6 + (πn)/2, n∈Z
Решение во вложениииииииииииииииииииииииииииииииии
<span>(x+1)²+(x-1)²=x²+2x+1+x²-2x+1=2x²+2=2·(x²+1)</span>
Арифметическая прогрессия
a1 = 20
d = 4
<span>n = 16
</span><span>S = (a1 +an)*n/2 = (2a1 + (n - 1)d)*n/2 = (2*20 + (16 - 1)*4)*16/2 = 800
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