Question: If $ \sin \theta =\frac{a}{\sqrt{a^{2}+b^{2}}}, $ then the value of $ \cot \theta $ will be.
Options:
A) $ \frac{b}{a} $
B) $ \frac{a}{b} $
C) $ \frac{a}{b}+1 $
D) $ \frac{b}{a}+1 $
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Answer:
Correct Answer: A
Solution:
- Given, $ \sin \theta =\frac{a}{\sqrt{a^{2}+b^{2}}} $
.(i)
We know that, $ \sin \theta =\frac{Perpendicular}{Hypotenuse} $
Now in $ \Delta ,ABC, $ $ \sin \theta =\frac{AB}{AC} $ …. (ii)
On comparing Eqs. (i) and (ii), we get
$ AB=a $ and $ AC=\sqrt{a^{2}+b^{2}} $
Now in $ \Delta ,ABC, $ by Pythagoras theorem, we have
$ AC^{2}=AB^{2}+BC^{2} $
$ {{(\sqrt{a^{2}+b^{2}})}^{2}}={{(a)}^{2}}+{{(BC)}^{2}} $
$ {{(BC)}^{2}}=a^{2}+b^{2}-a^{2} $
$ \Rightarrow $ $ BC^{2}=b^{2}\Rightarrow BC=b $
$ \Rightarrow $ $ \cot \theta =\frac{Base}{Perpendicular}=\frac{BC}{AB} $
On putting values, $ \cot \theta =\frac{b}{a} $