中4數學題2~(急)

2006-10-15 7:13 am

a)若二次方程px^2+(5p)+4=0有二重根,求p的值。

回答 (4)

2006-10-15 7:17 am

✔ 最佳答案

px^2 +(5p)+4 = 0
since the equation have double real root.
D = 0
b^2 - 4ac = 0
0 - 4(p)(5p+4) = 0
-20p^2 -16p = 0
-4p(5p+4) = 0
p = 0 or p = -4/5

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2006-10-15 6:11 pm

delta = 0
delta = 5^2 - 4*p*4 = 0
25-16p=0
p=25/16

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2006-10-15 7:19 am

delta = (5p)^2 - 4(p)(4) larger than 0
25p^2 - 16p larger than 0
p(25p-16) larger than 0
p larger than 0 or p smaller than (16/25)

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2006-10-15 7:17 am

delta = 0
delta = 5^2 - 4*p*4 = 0
25-16p=0
p=25/16

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