TS EAMCET · Maths · Quadratic Equation

If $\alpha, \beta, \gamma$ are the roots of $x^3+2 x^2-3 x-1=0$ then $\alpha^{-2}+\beta^{-2}+\gamma^{-2}=$

A 12
B 13
C 14
D 15

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Answer & Solution

Correct Answer

(B) 13

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Detailed explanation

If $\alpha, \beta, \gamma$ are the roots of $x^3+2 x^2-3 x-1=0$ then $\alpha^{-2}+\beta^{-2}+\gamma^{-2}=$ $\Rightarrow \quad \alpha+\beta+\gamma=-2$ ...(i) $\alpha \beta+\beta \gamma+\gamma \alpha=-3$ ...(ii) and $\alpha \beta \gamma=1$ ...(iii) On squaring equation…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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From TS EAMCET

Following lists contain reactions and their corresponding equilibrium constants at different temperatures:

List - I (Reaction)	List - II $(K_{p})$
$2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g) at 298 K$	$4.0 \times 10^{24}$
$2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g) at 700 K$	$3.0 \times 10^{4}$
$N_{2} O_{4} (g) ⇌ 2 {NO}_{2} (g) at 298 K$	$0.98$
$N_{2} O_{4} (g) ⇌ 2 {NO}_{2} (g) at 500 K$	$1700$

∆ H_{1}^{0} and ∆ H_{2}^{0}

are the standard enthalpies for the reactions

2 {SO}_{2} + O_{2} ⇌ 2 {SO}_{3} and N_{2} O_{4} ⇌ 2 {NO}_{2}

respectively, then:

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If \(\alpha, \beta, \gamma\) are the roots of \(x^3+2 x^2-3 x-1=0\) then \(\alpha^{-2}+\beta^{-2}+\gamma^{-2}=\)

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