I think it looks like a... circle?

Algebra Level 4

If real numbers x x and y y satisfy ( x + 5 ) 2 + ( y 12 ) 2 = 1 4 2 (x+5)^2+(y-12)^2=14^2 , then what is the minimum value of x 2 + y 2 x^2+y^2 ?


The answer is 1.

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4 solutions

Maharnab Mitra
May 5, 2014

Consider a circle x 2 + y 2 = c 2 x^2+y^2=c^2 .

The distance of the point of intersection of this circle with the given circle from the origin gives the value of x 2 + y 2 x^2+y^2 , i.e., c 2 c^2 . It can be easily seen from the figure that the point of intersection of the blue circle with the given circle gives the minimum distance from the origin.

The distance of ( 5 , 12 ) (-5,12) from the origin is 13 13 and the radius of the given circle is 14 14 . So, radius of the blue circle, i. e., c c is 1 1 . So, minimum value of x 2 + y 2 x^2+y^2 is 1 1 .

Eddie The Head
May 4, 2014

Solution outline: \textbf{Solution outline:}

The equation can be visualized as a circle centered at ( 5 , 12 ) (-5,12) and having radius 14 14 . So x 2 + y 2 x^{2}+y^{2} is clearly the square of the minimum distance of the circumference of the circle from the origin which is ( 14 13 ) 2 = 1 (14 - 13)^{2} = \boxed{1} .

I first answered 27 27 ... :P

Daniel Liu - 7 years, 1 month ago

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27 is the maximum of x^2 + y^2.

Rajen Kapur - 7 years, 1 month ago

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Yea, that's why I first answered that. Then, I realized my mistake and answered 1.

Daniel Liu - 7 years, 1 month ago

Damn, me too. Gotta hate it when I don't read things carefully...

Petru Lupsac - 7 years, 1 month ago

never mind!

Mayank Holmes - 7 years, 1 month ago

Me too .I misread minimum for maximum

Ronak Agarwal - 6 years, 11 months ago

I think the circle's centre is (-5,12).

mietantei conan - 7 years, 1 month ago

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a bit of typing mistake may have occurred.

Sheikh Asif Imran Shouborno - 7 years, 1 month ago

Can it be done using distance formula?

Siddharth Kumar - 7 years, 1 month ago
Dishank Malde
May 6, 2014

Put x + 5 = 14cos(theta) and y - 12 = 14sin(theta) Thus, x^2 + y^2 = 196cos^2(theta) + 25 - 140cos(theta) + 196sin^2(theta) + 144 + 336sin(theta) = 365 + 336sin(theta) -140cos(theta) Thus, minimum value = 365 - 364 = 1

Yes I like your method. It would be better if you use LaTeX :)

Christopher Boo - 7 years, 1 month ago

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Haha! Thanks and sorry for the inconvenience. :)

Dishank Malde - 7 years, 1 month ago

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sorry , but how did you find 364 ????

Aicha Smiley - 7 years ago

sorry , but how did you find 364 ????

Aicha Smiley - 7 years, 1 month ago
Marvin De Luna
May 10, 2014

Get the equation of the line containing the origin (0,0) and the center of the circle (-5,12)

Get the solutions (intersection) of the Circle and the line.

There will be two solution, but use only the coordinate near the origin.

( 5/13 , -12/13) --- this is the solution

x^2 + y^2 = (5/13) ^ 2 + (-12/13) ^ 2 = 1

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