r^2+18r+81=0

解答

r^{2} + 18 r + 81 = 0

r = - 9

求解步骤

r^{2} + 18 r + 81 = 0

使用求根公式求解

r_{1, 2} = \frac{- 18 \pm 1 8 ^{2} - 4 \cdot 1 \cdot 81}{2 \cdot 1}

1 8^{2} - 4 \cdot 1 \cdot 81 = 0

r_{1, 2} = \frac{- 18 \pm 0}{2 \cdot 1}

r = \frac{- 18}{2 \cdot 1}

\frac{- 18}{2 \cdot 1} = - 9

r = - 9

二次方程组的解是:

r = - 9