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MHT CET · Maths · Trigonometric Equations

The set of all possible values of \(\theta\) in the interval \((0, \pi)\) for which the points \((1,2)\) and \((\sin \theta, \cos \theta)\) lie on the same side of the line \(x+y=1\), is __________.

  1. A \(\left(0, \frac{\pi}{2}\right)\)
  2. B \(\left(0, \frac{\pi}{4}\right)\)
  3. C \(\left(0, \frac{3 \pi}{4}\right)\)
  4. D \(\left(\frac{\pi}{4}, \frac{3 \pi}{4}\right)\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\left(0, \frac{\pi}{2}\right)\)

Step-by-step Solution

Detailed explanation

for lying on the same side \((\sin \theta+\cos \theta-1)(1+2-1)>0\)
\(\Rightarrow \sin \theta+\cos \theta>1\)
\(\Rightarrow \frac{1}{\sqrt{2}} \sin \theta+\frac{1}{\sqrt{2}} \cos \theta>\frac{1}{\sqrt{2}}\)

\(\Rightarrow \sin \left(\theta+\frac{\pi}{4}\right)>\frac{1}{\sqrt{2}}\)
\(\Rightarrow \frac{\pi}{4} < \theta+\frac{\pi}{4} < \frac{3 \pi}{4}\)
\(\Rightarrow 0 < \theta < \frac{\pi}{2}\)