Moving Ellipse

Geometry Level 3

For y > 0 y>0 , the given curve 2 y 2 + x 2 = 64 2 y^2 + x^2 = 64 is moved 5 5 units to the right. Find the point of intersection ( x , y ) (x,y) , Submit your answer as x × y \lfloor x \times y \rfloor .


The answer is 13.

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1 solution

David Vreken
Oct 25, 2018

If the curve 2 y 2 + x 2 = 64 2y^2 + x^2 = 64 is moved 5 5 units to the right, its new equation is 2 y 2 + ( x 5 ) 2 = 64 2y^2 + (x - 5)^2 = 64 . The point of intersection ( x , y ) (x, y) is the solution to these two equations, which by subtraction gives x 2 ( x 5 ) 2 = 0 x^2 - (x - 5)^2 = 0 which solves to x = 5 2 x = \frac{5}{2} , and by substitution gives 2 y 2 + ( 5 2 ) 2 = 64 2y^2 + (\frac{5}{2})^2 = 64 which solves to a positive value of y = 462 4 y = \frac{\sqrt{462}}{4} .

Therefore, x × y = 5 2 × 462 4 = 13 \lfloor x \times y \rfloor = \lfloor \frac{5}{2} \times \frac{\sqrt{462}}{4} \rfloor = \boxed{13} .

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