Foiled once again

Algebra Level 1

The polynomial in two variables

f ( x , y ) = x y + 3 y 4 x 12 f(x,y) = xy + 3y - 4x -12

can be expressed as the product of two linear factors with integer coefficients, namely

f ( x , y ) = ( a x + b y + c ) ( d x + e y + f ) . f(x,y) = (ax + by + c) ( dx + ey + f).

Evaluate a + b + c + d + e + f |a+b+c| + |d+e+f| .


The answer is 7.

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14 solutions

Cid Moraes
Dec 20, 2013

Factoring give us x y + 3 y 4 x 12 = y ( x + 3 ) 4 ( x + 3 ) = ( x + 3 ) ( y 4 ) xy+3y-4x-12=y(x+3)-4(x+3)=(x+3)(y-4) so the sum is 1 + 0 + 3 + 0 + 1 4 = 7 |1+0+3|+|0+1-4|=7

Ajay Maity
Dec 20, 2013

Given,

f ( x , y ) = x y + 3 y 4 x 12 f(x, y) = xy + 3y - 4x - 12

f ( x , y ) = y ( x + 3 ) 4 ( x + 3 ) f(x, y) = y(x + 3) - 4(x + 3)

f ( x , y ) = ( y 4 ) ( x + 3 ) f(x, y) = (y - 4)(x + 3) ...... (1)

Also, it is given that f ( x , y ) f(x, y) can also be expressed as

f ( x , y ) = ( a x + b y + c ) ( d x + e y + f ) f(x, y) = (ax + by + c)(dx + ey + f) ...... (2)

Comparing equations (1) and (2), we have

a = 0 a = 0

b = 1 b = 1

c = 4 c = -4

d = 1 d = 1

e = 0 e = 0

f = 3 f = 3

So, a + b + c + d + e + f |a + b + c| + |d + e + f|

= 0 + 1 + ( 4 ) + 1 + 0 + 3 = |0 + 1 + (-4)| + |1 + 0 + 3|

= 3 + 4 = |-3| + |4|

= 3 + 4 = 3 + 4

= 7 = 7

That's the answer!

really good solution!!!

milind prabhu - 7 years, 3 months ago
Daniel Liu
Dec 20, 2013

By Simon's Favorite Factoring Trick, x y + 3 y 4 x 12 = ( x + 3 ) ( y 4 ) xy+3y-4x-12=(x+3)(y-4) . Therefore our answer is 1 + 0 + 3 + 1 + 0 + 4 = 7 |1+0+3|+|1+0+-4|=\boxed{7}

Forward, Simon!

Guilherme Dela Corte - 7 years, 5 months ago
Romeo Gomez
Dec 23, 2013

Doing the product we have f ( x , y ) = a d x 2 + b e y 2 + ( a e + b d ) x y + ( a f + c d ) x + ( b f + c e ) y + c f = x y + 3 y 4 x 12 f(x,y)=adx^2 + bey^2 + (ae+bd)xy + (af+cd)x + (bf +ce)y + cf=xy + 3y-4x-12 . Thus a f + c d = 4 b f + c e = 3 a e + b d = 1 c f = 12 af+cd=-4 \\ bf+ce=3\\ ae+bd=1\\ cf=-12 the last equation has four cases c = ± 3 , f = 4 c=\pm3, f=\mp4 but doesn't matter because we want the absolute value so we are going to say that c = 3 , f = 4 c=3, f=-4 and the system of equations is going to be like this, 4 a + 3 d = 4 4 b + 3 e = 3 a e + b d = 1 , -4a+3d=-4 \\ -4b+3e=3 \\ ae+bd=1, but a d = b e = 0 , ad=be=0, because we don't have square terms and say that a = e = 0. a=e=0. Substituting 3 d = 4 4 b = 3 b d = 1 , 3d=-4 \\ -4b=3\\ bd=1, from the last equation we solved it and obtein that b = d = ± 1 , b=d=\pm1, because the problem says that the coefficients are integers. So a = 0 b = ± 1 c = ± 3 d = ± 1 e = 0 f = 4 a=0 \\ b= \pm1 \\ c=\pm3 \\ d=\pm1 \\ e=0 \\ f=\mp4 . So (I'm tired at this point haha) a + b + c = 0 ± 1 ± 3 = ± 4 = 4 d + e + f = ± 1 + 0 4 = 3 = 3 |a+b+c|=|0 \pm1 \pm3|=|\pm4|=4 \\ |d+e+f|=|\pm1+0\mp4|=|\mp3|=3 and a + b + c + d + e + f = 4 + 3 = 7 |a+b+c| +|d+e+f|=4+3=\boxed{7}

Carl Denton
Dec 22, 2013

We find by inspection that f ( x , y ) = ( x + 3 ) ( y 4 ) f(x,y) = (x+3)(y-4) . Thus we simply plug in and find 3 + 4 = 7 3+4 = 7

It is a simple problem . JUST START CONSIDERING VALUES OR ASSUME.HERE I HAVE SIMPLY ASSUMED THAT a=1;b=0;c=3;d=0;e=1;f=-4 YOU FIND THIS BY SIMPLE ANALYSIS OF PROBLEM

Antony Diaz
Dec 21, 2013

First, we have that (ax+by+c)(dx+ey+f)=xy+3y-4x-12 (ad)x^{ 2 }+(be){ y }^{ 2 }+(ae+bd)xy+(af+cd)x+(bf+ce)y+cf=xy+3y-4x-12 So,it's sure that ad=0; be=0 and cf=-12. But as { a,b,c,d,e,f } are entiers, then c=3 and f=-4. So b and d are 1. Finally the absolue valeur is 7.

We can factorize the function to the form ( x + 3 ) ( y 4 ) (x+3)(y-4) . So we can conclude that a = e = 1 , b = d = 0 , c = 3 a=e=1, b=d=0, c=3 and f = 4 f=-4 . Thus, a + b + c + d + e + f = 1 + 0 + 3 + 0 + 1 + ( 4 ) = 4 + 3 = 4 + 3 = 7 |a+b+c|+|d+e+f|=|1+0+3|+|0+1+(-4)|=|4|+|-3|=4+3=7

Abishanka Saha
Dec 21, 2013

x y + 3 y 4 x 12 = ( x + 3 ) ( y 4 ) xy+3y-4x-12=(x+3)(y-4)

Meet Udeshi
Dec 21, 2013

The expression is so easy to factorize.

\f(x,y)=(x+3)(y-4)]

Thanic Samin
Dec 20, 2013

x y + 3 y 4 x 12 = ( x + 3 ) ( y 4 ) xy+3y-4x-12=(x+3)(y-4) This implies, a = 1 , b = 0 , c = 3 , d = 1 , e = 0 , f = 4 a=1,b=0,c=3,d=1,e=0,f=-4 , so the answer is 2 2

Aimee Polanco
Dec 20, 2013
  1. Group the terms so as to acquire common monomials. (xy + 3y) - (4x + 12)
  2. Factor out common terms y(x+3) - 4(x + 3)
  3. Combine the common terms and it will result to: (y-4) (x+3)

Add the coefficients and take the absolute values.

|1-3| + |1+3| = 7

Taisuke Yasuda
Dec 20, 2013

We can factor out y in the first two terms and -4 in the last two terms, giving us y(x+3) - 4(x+3). From this, we can further factor out (x+3), giving us (x+3)(y-4). Therefore, if we evaluate the expression |a + b + c| + |d + e + f|, we get |1+3| + |1-4| = 7.

Budi Utomo
Dec 20, 2013

(ax + by + c)( dx + ey + f) = xy - 4x + 3y -12 ---> adx^2 + aexy + afx + bdxy + bey^2 + bfy + cdx + cey + cf = xy - 4x + 3y -12 ---> adx^2 + (ae + bd)xy + bey^2 + (af + cd)x + (bf +ce)y + cf = 0.x^2 + 1xy + 0.y^2 - 4x + 3y - 12. Now , we have ad = 0, be = 0 , cf = - 12, ae + bd = 1, af + cd = - 4, bf + ce = 3 ; So we have solutions that are a = 0 , b = 1 , c = -4 , d = 1 , e = 0, f = 3. So the result of |a + b + c| + |d + e + f| = |0 + 1 + (-4)| + |1 + 0 + 3| = |-3| + |4| = 3 + 4 = 7. Answer : 7

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