"Spoooooooky" Russian rational expressions 11

Algebra Level 2

E = 1 ( 2 a 2 2 a + 2 ) ( a 3 a + 2 4 ) \mathscr{E} = 1- \left( \dfrac{2}{a-2} - \dfrac{2}{a+2} \right) \left( a-\dfrac{3a+2}{4} \right)

Let a = 2016 a = 2016 . If E \mathscr{E} can be expressed in the form x y \dfrac{x}{y} , where x x and y y are coprime positive integers , find x + y x+y .


Credit: My former Trig teacher's worksheet of Russian rational expressions


The answer is 2017.

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2 solutions

Hung Woei Neoh
Jul 6, 2016

E = 1 ( 2 a 2 2 a + 2 ) ( a 3 a + 2 4 ) = 1 ( 2 ( a + 2 ) 2 ( a 2 ) ( a 2 ) ( a + 2 ) ) ( 4 a ( 3 a + 2 ) 4 ) = 1 ( 8 2 ( a 2 ) ( a + 2 ) ) ( a 2 4 ) = 1 2 a + 2 \mathscr{E} = 1 - \left(\dfrac{2}{a-2}-\dfrac{2}{a+2}\right)\left(a-\dfrac{3a+2}{4}\right)\\ =1-\left(\dfrac{2(a+2)-2(a-2)}{(a-2)(a+2)}\right)\left(\dfrac{4a-(3a+2)}{4}\right)\\ =1-\left(\dfrac{\color{#D61F06}{\cancel{\color{#333333}{8}}2}}{\color{#3D99F6}{\cancel{\color{#333333}{(a-2)}}}(a+2)}\right)\left(\dfrac{\color{#3D99F6}{\cancel{\color{#333333}{a-2}}}}{\color{#D61F06}{\cancel{\color{#333333}{4}}}}\right)\\ =1-\dfrac{2}{a+2}

a = 2016 E = 1 2 2016 + 2 = 1 2 2018 = 1 1 1009 = 1008 1009 a=2016\\ \mathscr{E} = 1-\dfrac{2}{2016+2}=1-\dfrac{2}{2018}=1-\dfrac{1}{1009}=\dfrac{1008}{1009}

x = 1008 , y = 1009 , x + y = 1008 + 1009 = 2017 \implies x=1008,\;y=1009,\;x+y=1008+1009=\boxed{2017}

@Abhay Kumar see? Someone agrees with me. @Hung Woei Neoh Nice solution!

Hobart Pao - 4 years, 11 months ago

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What did I agree to?

Hung Woei Neoh - 4 years, 11 months ago

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Got it thanks!.

A Former Brilliant Member - 4 years, 11 months ago

You agree with my answer. Abhay feels my answer was wrong and reported the problem.

Hobart Pao - 4 years, 11 months ago

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@Hobart Pao No wonder this was the only one without a solution. The rest all have solutions written by Abhay

Hung Woei Neoh - 4 years, 11 months ago
Armain Labeeb
Jul 6, 2016

E = 1 ( 2 a 2 2 a + 2 ) ( a 3 a + 2 4 ) = 1 ( 2 ( a + 2 ) ( a 2 ) ( a + 2 ) 2 ( a 2 ) ( a + 2 ) ( a 2 ) ) ( 4 a 4 3 a + 2 4 ) = 1 ( 2 ( a + 2 ) 2 ( a 2 ) ( a 2 ) ( a + 2 ) ) ( 4 a ( 3 a + 2 ) 4 ) = 1 ( 2 a + 4 2 a + 4 ( a 2 ) ( a + 2 ) ) ( 4 a 3 a 2 4 ) = 1 ( 8 ( a 2 ) ( a + 2 ) ) ( ( a 2 ) 4 ) = 1 ( 8 ( a 2 ) 4 ( a 2 ) ( a + 2 ) ) = 1 ( 2 ( a + 2 ) ) = 1 2 2018 = 1009 1009 1 1009 = 1008 1009 x y = 1008 1009 x + y = 1008 + 1009 = 2017 \begin{aligned} \mathscr{ E } & =1-\left( \frac { 2 }{ a-2 } -\frac { 2 }{ a+2 } \right) \left( a-\frac { 3a+2 }{ 4 } \right) \\ & =1-\left( \frac { 2(a+2) }{ (a-2)(a+2) } -\frac { 2(a-2) }{ (a+2)(a-2) } \right) \left( \frac { 4a }{ 4 } -\frac { 3a+2 }{ 4 } \right) \\ & =1-\left( \frac { 2(a+2)-2(a-2) }{ (a-2)(a+2) } \right) \left( \frac { 4a-(3a+2) }{ 4 } \right) \\ & =1-\left( \frac { 2a+4-2a+4 }{ (a-2)(a+2) } \right) \left( \frac { 4a-3a-2 }{ 4 } \right) \\ & =1-\left( \frac { 8 }{ (a-2)(a+2) } \right) \left( \frac { (a-2) }{ 4 } \right) \\ & =1-\left( \frac { 8(a-2) }{ 4(a-2)(a+2) } \right) \\ & =1-\left( \frac { 2 }{ (a+2) } \right) \\ & =1-\frac { 2 }{ 2018 } \\ & =\frac { 1009 }{ 1009 } -\frac { 1 }{ 1009 } \\ & =\frac { 1008 }{ 1009 } \\ \therefore \quad \quad \quad \frac { x }{ y } & =\frac { 1008 }{ 1009 } \\ \longrightarrow x+y & =1008+1009=\boxed { 2017 } \end{aligned}\\

Err......I see no difference in the 5th and 6th lines...

Hung Woei Neoh - 4 years, 11 months ago

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Mistakes :P

Armain Labeeb - 4 years, 11 months ago

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