AP EAMCET · Maths · Quadratic Equation

Let $θ$ be an acute angle such that the equation $x^{3} + 4 x^{2} \cos θ + x \cot θ = 0$ has multiple roots. Then the value of $θ$ (in radians) is

A $\frac{π}{3}$
B $\frac{π}{8}$
C $\frac{π}{12}$ or $\frac{5 π}{12}$
D $\frac{π}{6}$ or $\frac{5 π}{12}$

Verified Solution

Answer & Solution

Correct Answer

(C) $\frac{π}{12}$ or $\frac{5 π}{12}$

Step-by-step Solution

Detailed explanation

The given equation is, x3+4x2cosθ+xcotθ=0 xx2+4xcosθ+cotθ=0 One root of the equation is x=0 and x2+4xcosθ+cotθ=0 has multiple solutions. So, discriminant, (4cosθ)2-4(1)cotθ=0 ⇒16cos2θ=4cotθ ⇒4cosθ=1sinθ or…

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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Let θ be an acute angle such that the equation x3+4x2cosθ+xcotθ=0 has multiple roots. Then the value of θ (in radians) is

Step-by-step Solution

Let $θ$ be an acute angle such that the equation $x^{3} + 4 x^{2} \cos θ + x \cot θ = 0$ has multiple roots. Then the value of $θ$ (in radians) is