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If X and Y are acute …

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If X and Y are acute angels such that sinX=1/√5 and sinY =1/√10 prove that (x+y)=π/4.

  • 1 answers

Naveen Sharma 8 years, 5 months ago

Ans. Given :  {tex}sin X = {1\over \sqrt 5}{/tex}{tex}sin Y = {1\over \sqrt {10}}{/tex}

X = {tex}sin^{-1}({1\over \sqrt 5}){/tex}

Y = {tex}sin^{-1}({1\over \sqrt {10}}){/tex}

=> X+Y = {tex}sin^{-1}({1\over \sqrt 5}) + sin^{-1}({1\over \sqrt {10}}){/tex}

{tex}[using \ \ sin^{-1} a + sin^{-1} b = sin^{-1}(a\sqrt{1-b^2}+b\sqrt{1-a^2})]{/tex}

{tex}=> X+Y = sin^{-1}\left ( {1\over \sqrt 5} \sqrt {1- {1\over 10}} + {1\over \sqrt {10}} \sqrt {1- {1\over 5}}\right ){/tex} 

{tex}=> X+Y = sin^{-1}\left ( {3\over \sqrt {50}} + {2\over \sqrt {50}} \right ){/tex}

{tex}=> X+Y = sin^{-1}\left ( {5\over 5\sqrt 2} \right ){/tex}

{tex}=> X+Y = sin^{-1}\left ( {1\over \sqrt 2} \right ){/tex}

{tex}=> X+Y = sin^{-1}\left ( sin {\pi \over 4} \right ){/tex}

{tex}=> X+Y = {\pi \over 4} {/tex}

Hence Proved

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