Only Ratio Matters!!!

Calculus Level 3

Let us define: \text{Let us define:}

I 1 = 0 π 2 1 + 1 1 + cot 2011 x d x I_{1}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1+\frac{1}{\sqrt[]{1+\cot ^{2011}x}}}dx

I 2 = 0 π 2 1 1 1 + cot 2011 x d x I_{2}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1-\frac{1}{\sqrt[]{1+\cot ^{2011}x}}}dx

F i n d ( I 1 I 2 ) 2 + ( I 2 I 1 ) 2 . Find~ \left( \frac{I_{1}}{I_{2}} \right) ^{2}+ \left( \frac{I_{2}}{I_{1}} \right) ^{2}.


The answer is 6.

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

Saket Raj
Jun 3, 2020

H e r e Here

I 1 = 0 π 2 1 + 1 1 + cot 2011 x d x I_{1}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1+\frac{1}{\sqrt[]{1+\cot ^{2011}x}}}dx

I 2 = 0 π 2 1 1 1 + cot 2011 x d x I_{2}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1-\frac{1}{\sqrt[]{1+\cot ^{2011}x}}}dx

L e t 1 1 + cot 2011 x = sin θ for some θ , s i n c e Let~\frac{1}{\sqrt[]{1+\cot ^{2011}x}}=\sin \theta ~ \text{for some} ~ \theta , since

1 1 + cot 2011 x <1 for x in ( 0 , π 2 ) \frac{1}{\sqrt[]{1+\cot ^{2011}x}}\text{<1 for x in } \left( 0,\frac{ \pi }{2} \right)

It can be easily proved that \text{It can be easily proved that }

cos θ = cot 2011 x 1 + cot 2011 x , u s i n g sin 2 θ + cos 2 θ = 1. \cos \theta =\frac{\sqrt[]{\cot ^{2011}x}}{\sqrt[]{1+\cot ^{2011}x}},using~\sin ^{2} \theta +\cos ^{2} \theta =1.

a l s o , I 1 = 0 π 2 1 + 1 1 + cot 2011 ( π 2 x ) d x also,~I_{1}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1+\frac{1}{\sqrt[]{1+\cot ^{2011} \left( \frac{ \pi }{2}-x \right) }}}dx

I 1 = 0 π 2 1 + cot 2011 x 1 + cot 2011 x d x I_{1}= \int _{0}^{\frac{ \pi }{2}}\sqrt[]{1+\frac{\sqrt[]{\cot ^{2011}x}}{\sqrt[]{1+\cot ^{2011}x}}}dx~

T h e r e f o r e , Therefore,

2 I 1 = 0 π / 2 ( 1 + 1 1 + cot 2011 x + 1 + cot 2011 x 1 + cot 2011 x ) d x 2I_{1}= \int _{0}^{ \pi /2} \left( \sqrt[]{1+\frac{1}{\sqrt[]{1+\cot ^{2011}x}}}+\sqrt[]{1+\frac{\sqrt[]{\cot ^{2011}x}}{\sqrt[]{1+\cot ^{2011}x}}} \right) dx

or, 2 I 1 = 0 π / 2 ( 1 + s i n θ + 1 + c o s θ ) d x . . ( 1 ) \text{or, 2}I_{1}= \int _{0}^{ \pi /2} \left( \sqrt[]{1+sin \theta }+\sqrt[]{1+cos \theta } \right) dx \ldots .. \left( 1 \right)

similarly, 2 I 2 = 0 π / 2 ( 1 s i n θ + 1 c o s θ ) d x . . ( 2 ) \text{similarly, 2}I_{2}= \int _{0}^{ \pi /2} \left( \sqrt[]{1-sin \theta }+\sqrt[]{1-cos \theta } \right) dx \ldots .. \left( 2 \right)

Now, for all θ in ( 0 , π 2 ) \text{ Now, for all}~ \theta~\text{ in }~ \left( 0,\frac{ \pi }{2} \right)

1 + s i n θ + 1 + c o s θ 1 s i n θ + 1 c o s θ = 2 + 1 \frac{\sqrt[]{1+sin \theta }+\sqrt[]{1+cos \theta }}{\sqrt[]{1-sin \theta }+\sqrt[]{1-cos} \theta }=\sqrt[]{2}+1

and hence it follows that \text{and hence it follows that}

I 1 I 2 = 2 + 1 \frac{I_{1}}{I_{2}}=\sqrt[]{2}+1

H e n c e ( I 1 I 2 ) 2 + ( I 2 I 1 ) 2 = 3 + 2 2 + 3 2 2 = 6. Hence~ \left( \frac{I_{1}}{I_{2}} \right) ^{2}+ \left( \frac{I_{2}}{I_{1}} \right) ^{2}=3+2\sqrt[]{2}+3-2\sqrt[]{2}=6.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...