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If one root of a(x^2)+bx+c=0 is the square of the other,then which of the following is true-options below?

A) a^3+b^3+c^3=3abc

B) a^2+b^2+c^2=3abc

C) (a^2)c+a(c^2)+b^3=3abc

D) (a^2)c+a(c^2)-b^3=3abc

please explain how u reached the conclusion

2 Answers

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  • ?
    Lv 5
    6 years ago
    Favorite Answer

    Let the roots be p and p^2.

    p + p^2 = -b/a

    (p) (p^2) = c/a, or, p^3 = c/a

    Now, 1 - p^3 = (1-p) (1+p+p^2)

    Or, 1 - (c/a) = (1-p) (1 - (b/a)).

    Or, (a-c)/a = (1-p) (a-b)/a

    Or, (a-c) = (1-p) (a-b)

    Or, (a-c) / (a-b) = (1-p)

    p = 1 - (1-p) = 1 - [(a-c) / (a-b)]

    = ((a-b) - (a-c)) / (a-b)

    = (c-b) / (a-b).... equation (1)

    Since p is a root of the given equation, it will satisfy it. So,

    ap^2 + bp + c = 0

    Or, a (a-b)^2 p^2 + b (a-b)^2 p + c (a-b)^2 = 0

    Or, a (c-b)^2 + b (c-b) (a-b) + c (a-b)^2 = 0 [by substituting the value of p using equation (1)]

    Or, a (c^2 - 2bc + b^2) + b (ca - ab - bc + b^2) + c (a^2 - 2ab + b^2) = 0

    Or, ac^2 - 2abc + ab^2 + abc - ab^2 - cb^2 + b^3 + ca^2 - 2abc + cb^2 = 0

    Or, ac^2 + b^3 + ca^2 = 3abc

    Hence, option C is correct.

  • Anonymous
    6 years ago

    Let "λ" be a root of the quadratic.

    The quadratic we are looking for is:

    (x - λ)(x - λ²) = 0

    x² - λ²x - λx + λ³ = 0

    x² + (-λ² - λ)x + λ³ = 0

    a = 1

    b = -λ² - λ

    c = λ³

    3abc = 3(1)(-λ² - λ)(λ³)

    3abc = -3λ⁵ - 3λ⁴

    That means the left side has to be of a power 5. The only answer that does this is D).

    EDIT: Nope, I was wrong. It is in fact option C).

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