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受欢迎的代数 >

completesquare 13r^2+52r+21=0

解答

13 r^{2} + 52 r + 21 = 0

解答

r = \frac{31}{13} - 2, r = - \frac{31}{13} - 2

+1

十进制

r = - 0.45578 \dots, r = - 3.54421 \dots

求解步骤

13 r^{2} + 52 r + 21 = 0

将

21

到右边

13 r^{2} + 52 r = - 21

两边除以

13

\frac{13 r ^{2} + 52 r}{13} = \frac{- 21}{13}

r^{2} + 4 r = - \frac{21}{13}

改写为形式

(x + a)^{2} = b

(r + 2)^{2} = \frac{31}{13}

若

f^{2} (x) = a

，解为

f (x) = a, - a

解

r + 2 = \frac{31}{13} : r = \frac{31}{13} - 2

解

r + 2 = - \frac{31}{13} : r = - \frac{31}{13} - 2

二次方程组的解是:

r = \frac{31}{13} - 2, r = - \frac{31}{13} - 2

作图

流行的例子

completesquare 7x^2+4x

co m pl e t es q u a re 7 x^{2} + 4 x

1 5^{2} = x^{2} + 9^{2}

solvefor x,(x-6)^2+(y-8)^2=k

so l v e f or x, (x - 6)^{2} + (y - 8)^{2} = k

solvefor x,x^2-y^2+2xy=0

so l v e f or x, x^{2} - y^{2} + 2 x y = 0

(a+2)(2a+4)(2)=5(4)(2)+156

(a + 2) (2 a + 4) (2) = 5 (4) (2) + 156