Math, asked by s1272adrija9914, 2 months ago

if cos thita = root 21/5 then find the value of 10+10 cot² thita​

Answers

Answered by MaheswariS
3

\textbf{Given:}

\mathsf{cos\theta=\dfrac{\sqrt{21}}{5}}

\textbf{To find:}

\textsf{The value of}\;\mathsf{10+10\,cot^2\theta}

\textbf{Solution:}

\textsf{Consider,}

\mathsf{cos\theta=\dfrac{\sqrt{21}}{5}}

\mathsf{Squaring\;on\;bothsids,\;we\;get}

\mathsf{cos^2\theta=\dfrac{21}{25}}

\implies\mathsf{sec^2\theta=\dfrac{25}{21}}

\textsf{We know that,}

\mathsf{tan^2\theta=sec^2\theta-1}

\mathsf{tan^2\theta=\dfrac{25}{21}-1}

\mathsf{tan^2\theta=\dfrac{4}{21}}

\implies\mathsf{cot^2\theta=\dfrac{21}{4}}

\mathsf{Now,}

\mathsf{10+10\,cot^2\theta}

\mathsf{=10(1+cot^2\theta)}

\mathsf{=10\left(1+\dfrac{21}{4}\right)}

\mathsf{=10\left(\dfrac{25}{4}\right)}

\mathsf{=5\left(\dfrac{25}{2}\right)}

\mathsf{=\dfrac{125}{2}}

\implies\boxed{\mathsf{10+10\,cot^2\theta=\dfrac{125}{2}}}

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