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If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)
  • a)
    a2 + c2 = – ab
  • b)
    a2 – c2 =  – ab
  • c)
    a2 – c2 = ab
  • d)
    none of these
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 =...
As (x2 + px + 1) is a factor of ax3 + bx + c, we can assume that zeros of  x2 + px + 1 are a, b and that of ax3 + bx + c be α, β, γ so that
α + β = – p .... (i)
αβ = 1 .... (ii)
and  α + β + γ = 0 .... (iii)
Solving (ii) and (v) we get γ = – c / a.
Also from (i) and (iii) we get γ = p
∴ p = g = – c / a Using equations (i) , (ii) and (iv) we get
  (using  γ = p = – c / a)
a2 – c2= ab
∴ (c) is the  correct answer.
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Most Upvoted Answer
If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 =...
We know that if $(x^2 + px + 1)$ is a factor of $(ax^3 + bx + c)$, then the roots of the quadratic equation $x^2 + px + 1 = 0$ are also roots of the cubic equation $ax^3 + bx + c = 0$.

Let the roots of the quadratic equation be $r$ and $s$. Then, we have $r + s = -p$ and $rs = 1$.

Since $r$ and $s$ are also roots of the cubic equation, we have $ar^3 + br + c = 0$ and $as^3 + bs + c = 0$.

Adding these two equations, we get $ar^3 + as^3 + br + bs + 2c = 0$. Since $r^3 = \frac{1}{r}$ and $s^3 = \frac{1}{s}$, this equation becomes $a(r + s)(rs) + b(r + s) + 2c = 0$.

Substituting $r + s = -p$ and $rs = 1$, we get $a(-p) + b(-p) + 2c = 0$, which simplifies to $-ap - bp + 2c = 0$.

Rearranging this equation, we have $2c = ap + bp$.

Squaring both sides, we get $(2c)^2 = (ap + bp)^2$, which simplifies to $4c^2 = (a^2 + 2ab + b^2)p^2$.

Since $ab = -1$, this equation becomes $4c^2 = (a^2 - 2 + b^2)p^2$.

Substituting $a^2 + b^2 = (a + b)^2 - 2ab = (p^2 - 2)^2 - 2$, we get $4c^2 = ((p^2 - 2)^2 - 2)p^2$.

Expanding and simplifying this equation, we have $4c^2 = p^4 - 4p^2 + 2p^2 - 2p^2$, which further simplifies to $4c^2 = p^4 - 4p^2$.

Dividing both sides by $p^2$, we get $4\left(\frac{c}{p}\right)^2 = p^2 - 4$.

Since $\left(\frac{c}{p}\right)^2$ is a nonnegative real number, $p^2 - 4$ must also be nonnegative. Therefore, $p^2 \geq 4$, which implies that $p \geq 2$ or $p \leq -2$.

Thus, we have $a^2 + c^2 = \boxed{1980}$.
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If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 = – abb)a2 – c2 = – abc)a2 – c2 = abd)none of theseCorrect answer is option 'C'. Can you explain this answer?
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If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 = – abb)a2 – c2 = – abc)a2 – c2 = abd)none of theseCorrect answer is option 'C'. Can you explain this answer? for JEE 2025 is part of JEE preparation. The Question and answers have been prepared according to the JEE exam syllabus. Information about If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 = – abb)a2 – c2 = – abc)a2 – c2 = abd)none of theseCorrect answer is option 'C'. Can you explain this answer? covers all topics & solutions for JEE 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for If (x2 + px + 1) is a factor of (ax3 + bx + c), then (1980)a)a2 + c2 = – abb)a2 – c2 = – abc)a2 – c2 = abd)none of theseCorrect answer is option 'C'. Can you explain this answer?.
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