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受欢迎的代数 >

(n(n-3))/2 =90

解答

\frac{n ( n - 3 )}{2} = 90

解答

n = 15, n = - 12

求解步骤

\frac{n ( n - 3 )}{2} = 90

在两边乘以

2

n (n - 3) = 180

展开

n (n - 3) : n^{2} - 3 n

n^{2} - 3 n = 180

将

180

para o lado esquerdo

n^{2} - 3 n - 180 = 0

使用求根公式求解

n_{1, 2} = \frac{- ( - 3 ) \pm ( - 3 ) ^{2} - 4 \cdot 1 \cdot ( - 180 )}{2 \cdot 1}

(- 3)^{2} - 4 \cdot 1 \cdot (- 180) = 27

n_{1, 2} = \frac{- ( - 3 ) \pm 27}{2 \cdot 1}

将解分隔开

n_{1} = \frac{- ( - 3 ) + 27}{2 \cdot 1}, n_{2} = \frac{- ( - 3 ) - 27}{2 \cdot 1}

n = \frac{- ( - 3 ) + 27}{2 \cdot 1} : 15

n = \frac{- ( - 3 ) - 27}{2 \cdot 1} : - 12

二次方程组的解是:

n = 15, n = - 12

作图

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