It's All Areas!

Geometry Level 4

Let A A be the sum of the areas of R 1 R_{1} and R 2 R_{2} .

If A = α α β ( λ arcsin ( ω λ ) γ arcsin ( α γ ) ) A = \dfrac{\alpha^{\alpha}}{\sqrt{\beta}} \left (\lambda\arcsin \left (\sqrt{\dfrac{\omega}{\lambda}} \right ) - \gamma\arcsin\left (\sqrt{\dfrac{\alpha}{\gamma}}\right )\right) , where α , β , λ , ω \alpha,\beta,\lambda,\omega and γ \gamma are coprime positive integers, find α + β + λ + ω + γ \alpha + \beta + \lambda + \omega + \gamma .


The answer is 23.

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1 solution

Rocco Dalto
Jan 29, 2021

x 2 + x y + y 2 = 7 x^2 + xy + y^2 = 7

x 2 x y + y 2 = 5 x^2 - xy + y^2 = 5

The coefficient( x 2 x^2 ) = coefficient( y 2 y^2 ) = 1 θ = 4 5 = 1 \implies \theta = 45^{\circ} and the equations of rotation are :

x = 1 2 x 1 2 y x = \dfrac{1}{\sqrt{2}}x' - \dfrac{1}{\sqrt{2}}y'

y = 1 2 x + 1 2 y y = \dfrac{1}{\sqrt{2}}x' + \dfrac{1}{\sqrt{2}}y'

Replacing ( x , y ) (x,y) in the initial equations we obtain:

x 2 + 3 y 2 = 10 x'^2 + 3y'^2 = 10

3 x 2 + y 2 = 14 3x'^2 + y'^2 = 14

Solving the above system we obtain x = ± 2 x' = \pm 2 (We only need x x' here) and

y 2 ( x ) = 14 3 x 2 y_{2}(x') = \sqrt{14 - 3x'^2} and y 1 ( x ) = 10 x 2 3 A 1 = 2 2 y 2 ( x ) y 1 ( x ) d x = A 2 y_{1}(x') = \dfrac{\sqrt{10 - x'^2}}{\sqrt{3}} \implies A_{1} = \displaystyle\int_{-2}^{2} y_{2}(x') - y_{1}(x') dx' = A_{2} .

I 1 = 2 2 y 2 ( x ) d x = 2 2 14 3 x 2 d x I_{1} = \displaystyle\int_{-2}^{2} y_{2}(x') dx' = \displaystyle\int_{-2}^{2} \sqrt{14 - 3x'^2} dx'

Letting 3 x = 14 sin ( θ ) 3 d x = 14 cos ( θ ) d θ \sqrt{3}x' = \sqrt{14}\sin(\theta) \implies \sqrt{3} dx' = \sqrt{14}\cos(\theta) d\theta \implies

I 1 = 7 3 ( arcsin ( 3 14 x ) + 3 x 14 3 x 2 14 ) 2 2 = I_{1} = \dfrac{7}{\sqrt{3}}(\arcsin(\dfrac{\sqrt{3}}{\sqrt{14}}x') + \dfrac{\sqrt{3}x'\sqrt{14 - 3x'^2}}{14})|_{-2}^{2} = 14 3 ( arcsin ( 6 7 ) + 6 7 ) \dfrac{14}{\sqrt{3}}(\arcsin(\sqrt{\dfrac{6}{7}}) + \dfrac{\sqrt{6}}{7})

and

I 2 = 2 2 y 1 ( x ) d x = 1 3 2 2 10 x 2 d x I_{2} = \displaystyle\int_{-2}^{2} y_{1}(x') dx' = \dfrac{1}{\sqrt{3}}\displaystyle\int_{-2}^{2} \sqrt{10 - x'^2} dx'

Letting x = 10 sin ( θ ) d x = 10 cos ( θ ) d θ x' = \sqrt{10}\sin(\theta) \implies dx' = \sqrt{10}\cos(\theta) d\theta \implies

I 2 = 5 3 ( arcsin ( x 10 ) + x 10 x 2 10 ) 2 2 = I_{2} = \dfrac{5}{\sqrt{3}}(\arcsin(\dfrac{x'}{\sqrt{10}}) + \dfrac{x'\sqrt{10 - x'^2}}{10})|_{-2}^{2} = 10 3 ( arcsin ( 2 5 ) + 6 5 ) \dfrac{10}{\sqrt{3}}(\arcsin(\sqrt{\dfrac{2}{5}}) + \dfrac{\sqrt{6}}{5})

A ! = I 1 I 2 = 2 3 ( 7 arcsin ( 6 7 ) 5 arcsin ( 2 5 ) ) = A 2 \implies A_{!} = I_{1} - I_{2} = \dfrac{2}{\sqrt{3}}(7\arcsin(\sqrt{\dfrac{6}{7}}) - 5\arcsin(\sqrt{\dfrac{2}{5}})) = A_{2}

A = A 1 + A 2 = 4 3 ( 7 arcsin ( 6 7 ) 5 arcsin ( 2 5 ) ) = \implies A = A_{1} + A_{2} = \dfrac{4}{\sqrt{3}}(7\arcsin(\sqrt{\dfrac{6}{7}}) - 5\arcsin(\sqrt{\dfrac{2}{5}})) =

α α β ( λ arcsin ( ω λ ) γ arcsin ( α γ ) ) α + β + λ + ω + γ = 23 \dfrac{\alpha^{\alpha}}{\sqrt{\beta}}(\lambda\arcsin(\sqrt{\dfrac{\omega}{\lambda}}) - \gamma\arcsin(\sqrt{\dfrac{\alpha}{\gamma}})) \implies \alpha + \beta + \lambda + \omega + \gamma = \boxed{23}

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