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受欢迎的代数 >

a=2pir(r+7)

解答

a = 2 π r (r + 7)

解答

r = \frac{- 7 π + π ( 2 a + 49 π )}{2 π}, r = - \frac{π ( 2 a + 49 π ) + 7 π}{2 π}

求解步骤

a = 2 π r (r + 7)

展开

2 π r (r + 7) : 2 π r^{2} + 14 π r

a = 2 π r^{2} + 14 π r

交换两边

2 π r^{2} + 14 π r = a

将

a

para o lado esquerdo

2 π r^{2} + 14 π r - a = 0

使用求根公式求解

r_{1, 2} = \frac{- 14 π \pm ( 14 π ) ^{2} - 4 \cdot 2 π ( - a )}{2 \cdot 2 π}

化简

(14 π)^{2} - 4 \cdot 2 π (- a) : 2 π (49 π + 2 a)

r_{1, 2} = \frac{- 14 π \pm 2 π ( 49 π + 2 a )}{2 \cdot 2 π}

将解分隔开

r_{1} = \frac{- 14 π + 2 π ( 49 π + 2 a )}{2 \cdot 2 π}, r_{2} = \frac{- 14 π - 2 π ( 49 π + 2 a )}{2 \cdot 2 π}

r = \frac{- 14 π + 2 π ( 49 π + 2 a )}{2 \cdot 2 π} : \frac{- 7 π + π ( 2 a + 49 π )}{2 π}

r = \frac{- 14 π - 2 π ( 49 π + 2 a )}{2 \cdot 2 π} : - \frac{π ( 2 a + 49 π ) + 7 π}{2 π}

二次方程组的解是:

r = \frac{- 7 π + π ( 2 a + 49 π )}{2 π}, r = - \frac{π ( 2 a + 49 π ) + 7 π}{2 π}

作图

流行的例子

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