Looks like what?

Geometry Level 3

Let N N and M M be two real numbers such that

N = tan 20 + tan 40 + 3 × tan 20 tan 40 N=\tan{20}+\tan{40}+\sqrt{3}\times \tan{20}\tan{40}

M = cot 16 cot 44 + cot 44 cot 76 cot 76 cot 16 M=\cot{16}\cot{44}+\cot{44}\cot{76}-\cot{76}\cot{16}

Find the value of M N 2 \dfrac M{N^2} .

None of these choices 3 \sqrt{3} 2 2 1 1 3 3

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Sabhrant Sachan
May 16, 2016

Let's Evaluate N \color{#3D99F6}N First. Using Trigonometric Identity

tan ( A + B ) = tan A + tan B 1 tan A × tan B \tan{(A+B)}=\dfrac{\tan{A}+\tan{B}}{1-\tan{A}\times\tan{B}}

tan ( 40 + 20 ) = tan 40 + tan 20 1 tan 40 tan 20 tan 40 + tan 20 = tan 60 ( 1 tan 40 tan 20 ) tan 40 + tan 20 = 3 3 tan 40 tan 20 N = 3 = tan 40 + tan 20 + 3 tan 40 tan 20 \tan{(40+20)}=\dfrac{\tan{40}+\tan{20}}{1-\tan{40}\tan{20}} \implies \tan{40}+\tan{20}=\tan{60}(1-\tan{40}\tan{20}) \\ \tan{40}+\tan{20}=\sqrt{3}-\sqrt{3}\tan{40}\tan{20} \\ \color{#3D99F6}N=\boxed{\sqrt{3}}=\tan{40}+\tan{20}+\sqrt{3}\tan{40}\tan{20}

To Find the Value of M \color{#20A900}M . We will use the identity of cot ( A + B ) \cot{(A+B)} and cot ( A B ) \cot{(A-B)}

cot ( A ± B ) = cot B × cot A 1 cot B ± cot A cot ( 16 + 44 ) = cot 44 cot 16 1 cot 44 + cot 16 cot 44 cot 16 = 1 3 ( cot 44 + cot 16 ) + 1 cot ( 44 + 76 ) = cot 76 cot 44 1 cot 76 + cot 44 cot 76 cot 44 = 1 3 ( cot 76 + cot 44 ) + 1 cot ( 76 16 ) = cot 16 cot 76 + 1 cot 16 cot 76 cot 16 cot 76 = 1 3 ( cot 16 cot 76 ) 1 cot 16 cot 76 = 1 3 ( cot 76 cot 16 ) + 1 M = cot 16 cot 44 + cot 44 cot 76 cot 76 cot 16 M = 1 3 ( cot 44 + cot 16 ) + 1 + 1 3 ( cot 76 cot 16 ) 1 3 ( cot 76 + cot 44 ) + 1 = 3 M N 2 = 1 \cot{(A\pm B)}=\dfrac{\cot{B}\times\cot{A}\mp1}{\cot{B}\pm\cot{A}} \\ \cot{(16+44)}=\dfrac{\cot{44}\cot{16}-1}{\cot{44}+\cot{16}} \\ \implies \cot{44}\cot{16}=\dfrac1{\sqrt3}(\cot{44}+\cot{16})+1\\ \cot{(44+76)}=\dfrac{\cot{76}\cot{44}-1}{\cot{76}+\cot{44}} \\ \implies \cot{76}\cot{44}= -\dfrac1{\sqrt3}(\cot{76}+\cot{44})+1\\ \cot{(76-16)}=\dfrac{\cot{16}\cot{76}+1}{\cot{16}-\cot{76}} \\ \implies \cot{16}\cot{76}=\dfrac1{\sqrt3}(\cot{16}-\cot{76})-1 \\ \implies -\cot{16}\cot{76}=\dfrac1{\sqrt3}(\cot{76}-\cot{16})+1 \\ \color{#20A900}M=\cot{16}\cot{44}+\cot{44}\cot{76}-\cot{76}\cot{16} \\ \implies \color{#20A900}M=\dfrac1{\sqrt3}(\cot{44}+\cot{16})+1+\dfrac1{\sqrt3}(\cot{76}-\cot{16})-\dfrac1{\sqrt3}(\cot{76}+\cot{44})+1 = \boxed{3} \\ \dfrac{\color{#20A900}M}{\color{#3D99F6}N^2}=\boxed{1}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...