Дана арифметическая прогрессия: -4,-2,0..найдите сумму первых десяти ее членов.
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2
a2=-2
d=a2-a1=-2 - (-4)=-2+4=2
S={ (2a1+ (n-1)*d)*n/2
S10={2*-4+(10-1)*2*10)/2=(-8+18)*10/2=10*10/2=100/2=50