Challenge!

I have answered you this question in the supplementary in your last question
http://hk.knowledge.yahoo.com/question/?qid=7006122600411

I will restate it here.

Let α and 5α be the roots.
Then α + 5α = -b/a
α = -b/(6a) ---(1)
and α(5α) = c/a
5α² = c/a ---(2)

Sub. (1) into (2),
5[-b/(6a)]² = c/a
5b² = c/a * 36a²
5b² = 36ac

The answer is (a).


Hope it helps! ^^
Wish you a Happy 2007!

let the roots be n & 5n

sum of roots = 6n
product of roots = 5n^2

-b / a = 6n
b^2 / a^2 = 36n^2 .....(1)

c / a = 5n^2 ......(2)


(1) / (2):
(b^2)(a) / (a^2)(c) = 36 / 5
(b^2) / ac = 36 / 5
5b^2 = 36ac

SO, the answer is (a)