AP EAMCET · Maths · Trigonometric Equations

The set of solutions of the system of equations
\[
\begin{aligned}
x+y & =\frac{2 \pi}{3} \\
\text { and } \quad \cos x+\cos y & =\frac{3}{2},
\end{aligned}
\]
where \(x, y\) are real, is

A \(\left\{(x, y): \cos \left(\frac{x-y}{2}\right)=\frac{1}{2}\right\}\)
B \(\left\{(x, y): \sin \left(\frac{x-y}{2}\right)=\frac{1}{2}\right\}\)
C \(\left\{(x, y): \cos (x-y)=\frac{1}{2}\right\}\)
D Empty set

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Answer & Solution

Correct Answer

(D) Empty set

Step-by-step Solution

Detailed explanation

Given system of equation is \[ x+y=\frac{2 \pi}{3} \] and \(\cos x+\cos y=\frac{3}{2}\), where \(x, y\) are real.…

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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The set of solutions of the system of equations\[\begin{aligned}x+y & =\frac{2 \pi}{3} \\\text { and } \quad \cos x+\cos y & =\frac{3}{2},\end{aligned}\]where \(x, y\) are real, is

Step-by-step Solution

The set of solutions of the system of equations
\[
\begin{aligned}
x+y & =\frac{2 \pi}{3} \\
\text { and } \quad \cos x+\cos y & =\frac{3}{2},
\end{aligned}
\]
where \(x, y\) are real, is