tim so nguyen x thoa man -210=-1+-2+-3+...+(-x-1)+-x la
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tim so nguyen x thoa man : -210=(-1)+(-2)+(-3)+...+(-x-1)+(-x)
-210 = (-1) + (-2) + .... + (-x - 1) + (-x)
-210 = -[1 + 2 + 3 + ..... + (x + 1) + x]
=> 210 = 1 + 2 + 3 + .... + (x + 1) + x
Áp dụng công thức tính dãy số ta có :
\(\frac{\left[\left(x-1\right):1+1\right].\left(x+1\right)}{2}=210\)
=> x(x + 1) = 420
=> x = 20
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Có -210 = (-1) + (-2) + (-3) +...+ (-x-1) + (-x)
=> -210 = -(1 + 2 + 3 +...+ (x-1) + x)
=> 210 = 1 + 2 + 3 +...+ (x-1) + x
=> 210 = (1+x)x : 2
=> 420 = x(x+1)
=> x = 20
Vậy x = 20. k nha bạn
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tim so nguyen x thoa man -210=(-1)+(-2)+(-3)+...+(-x+1)+(-x)
tim so nguyen x thoa man :
-210=(-1)+(-2)+(-3)+...+(-x+1)+(-x)
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