12th Class Mathematics Sample Paper Mathematics Sample Paper-8

  • question_answer
    Find an angle \[\theta \] which increases twice as fast as its sine.

    Answer:

    Let \[\theta \] denote the angle at instant t. \[\frac{d\theta }{dt}=2\frac{d}{dt}(sin\theta )\]                          [given] \[\Rightarrow \]   \[\frac{d\theta }{dt}=2\cos \theta \left( \frac{d\theta }{dt} \right)\] \[\Rightarrow \]   \[1=2\cos \theta \] \[\Rightarrow \]   \[2\cos \theta =1\] \[\Rightarrow \]   \[\cos \theta =\frac{1}{2}\] \[\Rightarrow \]   \[\theta ={{\cos }^{-1}}\left( \frac{1}{2} \right)=\frac{\pi }{3}.\] Hence, the required angles is \[\frac{\pi }{3}.\]


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