MATHS F.4 THX!!!

👨🏻‍🏫 學術台數學

yan

2010-07-03 4:05 am

1.If the equation X^2+k=0 has real roots,then

A.K＞0
B.K＜0
C.K>=0
D.K<=0

ANS is D

點計出黎???

THX!!!

回答 (2)

Prof. Physics

2010-07-03 4:11 am

✔ 最佳答案

For the quadratic equation x^2 + k = 0 has real roots,

the discriminant >= 0

So, 0 - 4(1)k >= 0

-4k >= 0

k <= 0

The answer is D.

參考: Prof. Physics

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用戶36565

2010-07-03 4:22 am

X^2+k=0 -------(1)
Then, X^2=-k

因為equation (1) 有 real root,
從X^2=-k, 可以得出:
X=開方根(-k)
而凡一個數打開方根, 嗰個數都要大於或等於零.
所以, (-k) >=0
(-k)+k>=0+k
0>=k
k<=0

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