The polynomial in two variables
f ( x , y ) = x y + 3 y − 4 x − 1 2
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 ) .
Evaluate ∣ a + b + c ∣ + ∣ d + e + f ∣ .
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Given,
f ( x , y ) = x y + 3 y − 4 x − 1 2
f ( x , y ) = y ( x + 3 ) − 4 ( x + 3 )
f ( x , y ) = ( y − 4 ) ( x + 3 ) ...... (1)
Also, it is given that f ( x , y ) can also be expressed as
f ( x , y ) = ( a x + b y + c ) ( d x + e y + f ) ...... (2)
Comparing equations (1) and (2), we have
a = 0
b = 1
c = − 4
d = 1
e = 0
f = 3
So, ∣ a + b + c ∣ + ∣ d + e + f ∣
= ∣ 0 + 1 + ( − 4 ) ∣ + ∣ 1 + 0 + 3 ∣
= ∣ − 3 ∣ + ∣ 4 ∣
= 3 + 4
= 7
That's the answer!
really good solution!!!
By Simon's Favorite Factoring Trick, x y + 3 y − 4 x − 1 2 = ( x + 3 ) ( y − 4 ) . Therefore our answer is ∣ 1 + 0 + 3 ∣ + ∣ 1 + 0 + − 4 ∣ = 7
Forward, Simon!
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 − 1 2 . Thus a f + c d = − 4 b f + c e = 3 a e + b d = 1 c f = − 1 2 the last equation has four cases c = ± 3 , f = ∓ 4 but doesn't matter because we want the absolute value so we are going to say that 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 , but a d = b e = 0 , because we don't have square terms and say that a = e = 0 . Substituting 3 d = − 4 − 4 b = 3 b d = 1 , from the last equation we solved it and obtein that b = d = ± 1 , because the problem says that the coefficients are integers. So a = 0 b = ± 1 c = ± 3 d = ± 1 e = 0 f = ∓ 4 . So (I'm tired at this point haha) ∣ a + b + c ∣ = ∣ 0 ± 1 ± 3 ∣ = ∣ ± 4 ∣ = 4 ∣ d + e + f ∣ = ∣ ± 1 + 0 ∓ 4 ∣ = ∣ ∓ 3 ∣ = 3 and ∣ a + b + c ∣ + ∣ d + e + f ∣ = 4 + 3 = 7
We find by inspection that f ( x , y ) = ( x + 3 ) ( y − 4 ) . Thus we simply plug in and find 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
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 ) . So we can conclude that a = e = 1 , b = d = 0 , c = 3 and f = − 4 . Thus, ∣ a + b + c ∣ + ∣ d + e + f ∣ = ∣ 1 + 0 + 3 ∣ + ∣ 0 + 1 + ( − 4 ) ∣ = ∣ 4 ∣ + ∣ − 3 ∣ = 4 + 3 = 7
x y + 3 y − 4 x − 1 2 = ( x + 3 ) ( y − 4 )
The expression is so easy to factorize.
\f(x,y)=(x+3)(y-4)]
x y + 3 y − 4 x − 1 2 = ( x + 3 ) ( y − 4 ) This implies, a = 1 , b = 0 , c = 3 , d = 1 , e = 0 , f = − 4 , so the answer is 2
Add the coefficients and take the absolute values.
|1-3| + |1+3| = 7
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.
(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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Factoring give us x y + 3 y − 4 x − 1 2 = y ( x + 3 ) − 4 ( x + 3 ) = ( x + 3 ) ( y − 4 ) so the sum is ∣ 1 + 0 + 3 ∣ + ∣ 0 + 1 − 4 ∣ = 7