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受欢迎的代数 >

1/5 k(k+4)=0.75

解答

\frac{1}{5} k (k + 4) = 0.75

解答

k = \frac{- 4 + 31}{2}, k = - \frac{4 + 31}{2}

+1

十进制

k = 0.78388 \dots, k = - 4.78388 \dots

求解步骤

\frac{1}{5} k (k + 4) = 0.75

在两边乘以

100

20 k (k + 4) = 75

展开

20 k (k + 4) : 20 k^{2} + 80 k

20 k^{2} + 80 k = 75

将

75

para o lado esquerdo

20 k^{2} + 80 k - 75 = 0

使用求根公式求解

k_{1, 2} = \frac{- 80 \pm 8 0 ^{2} - 4 \cdot 20 ( - 75 )}{2 \cdot 20}

8 0^{2} - 4 \cdot 20 (- 75) = 2031

k_{1, 2} = \frac{- 80 \pm 20 31}{2 \cdot 20}

将解分隔开

k_{1} = \frac{- 80 + 20 31}{2 \cdot 20}, k_{2} = \frac{- 80 - 20 31}{2 \cdot 20}

k = \frac{- 80 + 20 31}{2 \cdot 20} : \frac{- 4 + 31}{2}

k = \frac{- 80 - 20 31}{2 \cdot 20} : - \frac{4 + 31}{2}

二次方程组的解是:

k = \frac{- 4 + 31}{2}, k = - \frac{4 + 31}{2}

作图

流行的例子

(x - 1) (x + 9) = 0

x^{2} + 2 x^{2} = 1

x^{2} - 6 x + a = 0

(x - 1) (2 x + 2) = 0

1/4 x^2=-1/2 x+2

\frac{1}{4} x^{2} = - \frac{1}{2} x + 2