Quantitative Aptitude Ques 2485

Question: If $ 2\sin \theta =\sec \theta , $ what is the value of $ {{\sin }^{4}}\theta +{{\cos }^{4}}\theta ? $

Options:

A) 1

B) $ \frac{1}{2} $

C) $ \frac{1}{4} $

D) $ \frac{1}{8} $

Show Answer

Answer:

Correct Answer: B

Solution:

  • $ 2\sin \theta =\sec \theta $

$ \Rightarrow $ $ 2\sin \theta \cos \theta =1 $

$ \Rightarrow $ $ \sin 2\theta =1 $
$ \Rightarrow $ $ \sin 2\theta =sin90{}^\circ $

$ \Rightarrow $ $ 2\theta =90{}^\circ $
$ \Rightarrow $ $ \theta =45{}^\circ $

$ \therefore $ $ {{\sin }^{4}}\theta +{{\cos }^{4}}\theta ={{( \frac{1}{\sqrt{2}} )}^{4}}+{{( \frac{1}{\sqrt{2}} )}^{4}}=\frac{1}{2} $