quadraticformula x^2-4x=21

解

x^{2} - 4 x = 21

x = 7, x = - 3

解答ステップ

x^{2} - 4 x = 21

21

を左側に移動します

x^{2} - 4 x - 21 = 0

解くとthe二次式

x_{1, 2} = \frac{- ( - 4 ) \pm ( - 4 ) ^{2} - 4 \cdot 1 \cdot ( - 21 )}{2 \cdot 1}

(- 4)^{2} - 4 \cdot 1 \cdot (- 21) = 10

x_{1, 2} = \frac{- ( - 4 ) \pm 10}{2 \cdot 1}

解を分離する

x_{1} = \frac{- ( - 4 ) + 10}{2 \cdot 1}, x_{2} = \frac{- ( - 4 ) - 10}{2 \cdot 1}

x = \frac{- ( - 4 ) + 10}{2 \cdot 1} : 7

x = \frac{- ( - 4 ) - 10}{2 \cdot 1} : - 3

二次equationの解:

x = 7, x = - 3