There are enough points, but how do you determine the equation?

Algebra Level 5

There is a hyberbola that passes through points

A = ( 0 , 6 ) A = (0, 6)

B = ( 1 , 3 ) B = (1, 3)

C = ( 3 , 1 ) C = (3, 1)

D = ( 6 , 0 ) D = (6, 0)

E = ( 10 , 1 ) E = (10, -1)

If the equation for this hyperbola can be represented as

a x 2 + b y 2 + c x y + d x + e y + f = 0 ax^2 + by^2 + cxy + dx + ey + f = 0

where the gcd ( a , b , c , d , e , f ) \gcd (a, b, c, d, e, f) is 1, find the minimum value of

a + b + c + d + e + f a + b + c + d + e + f


The answer is -62.

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2 solutions

Aditya Raut
Aug 8, 2014

From the given points, we get the following equations

36 b + 6 e + f = 0 36b + 6e+f=0

36 a + 6 d + f = 0 36a+6d+f=0

a + 9 b + 3 c + d + 3 e + f = 0 a+9b+3c+d+3e+f=0

9 a + b + 3 c + 3 d + e + f = 0 9a+b+3c+3d+e+f=0

100 a + b 10 c + 10 d e + f = 0 100a+b-10c+10d-e+f=0


These are 5 5 equations and 6 6 variables, so you can't get values of all of them exactly. But we can eliminate 5 5 variables, giving each variable in terms of the 6 t h 6^{th} variable. After getting each variable in terms of a a (Which is a long algebraic manipulation, too long to type), we get

b = a , c = 52 a 11 , d = e = 65 a 11 , f = 6 11 b=a , c=\dfrac{52a}{11} , d=e=\dfrac{-65a}{11} , f = \dfrac{-6}{11}


Now, as a given statement is g c d ( a , b , c , d , e , f ) = 1 gcd(a,b,c,d,e,f)=1 , we conclude that a , b , c , d , e , f a,b,c,d,e,f are integers, so for smallest value, we will multiply it by 11 directly (no one said it should be positive)

Giving a = 11 , b = 11 , c = 52 , d = 65 , e = 65 , f = 6 a=11, b=11 , c=52 , d=-65 , e =-65, f =-6

They all sum up to give 62 \boxed{-62}

Note:- Using this wolfram alpha input is easier but cheating way.

Michael Mendrin
Aug 6, 2014

You need to specify an unique answer. As the problem is stated now, both 62 62 and 62 -62 are correct answers.

I changed the question. How that slipped by me, I do not know.

Sharky Kesa - 6 years, 10 months ago

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