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受欢迎的代数 >

(n(n+1))/2 =210

解答

\frac{n ( n + 1 )}{2} = 210

解答

n = 20, n = - 21

求解步骤

\frac{n ( n + 1 )}{2} = 210

在两边乘以

2

n (n + 1) = 420

展开

n (n + 1) : n^{2} + n

n^{2} + n = 420

将

420

para o lado esquerdo

n^{2} + n - 420 = 0

使用求根公式求解

n_{1, 2} = \frac{- 1 \pm 1 ^{2} - 4 \cdot 1 \cdot ( - 420 )}{2 \cdot 1}

1^{2} - 4 \cdot 1 \cdot (- 420) = 41

n_{1, 2} = \frac{- 1 \pm 41}{2 \cdot 1}

将解分隔开

n_{1} = \frac{- 1 + 41}{2 \cdot 1}, n_{2} = \frac{- 1 - 41}{2 \cdot 1}

n = \frac{- 1 + 41}{2 \cdot 1} : 20

n = \frac{- 1 - 41}{2 \cdot 1} : - 21

二次方程组的解是:

n = 20, n = - 21

作图

流行的例子

\frac{2}{2 - x} \leq \frac{4}{x}

4 (2 x - 2) = 8

x^{2} = \frac{1}{9}

- x^{2} + 8 x + 4 = 0

因式分解 25k^2-4

f a c t or 25 k^{2} - 4