Find the value of k if the quadratic equations has a double real root.
x^2 + 4kx + 16k + 20 = 0
answer is -1, 5
-1 我計到, 但 5 計不到
請列式如何計, thanks a lot!
Maths題不識, pls. help
2008-08-15 9:20 am
回答 (2)
2008-08-15 9:33 am
✔ 最佳答案
x^2 + 4kx + 16k + 20 = 0∆=0
(4k)^2-4(16k+20)=0
16k^2-64k-80=0
k^2-4k-5=0
(k-5)(k+1)=0
k=5 or k=-1
2008-08-15 9:32 am
(4k)^2-4(16k+20)=0
k^2-4k-5=0
k=(4-sqrt(16+4*5))/2 or (4+sqrt(16+4*5))/2
k=-1 or 5
k^2-4k-5=0
k=(4-sqrt(16+4*5))/2 or (4+sqrt(16+4*5))/2
k=-1 or 5
參考: myself
收錄日期: 2021-04-22 00:36:37
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