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x,y,z are consecutive integers (x<y<z). Which of the following

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x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 06:40
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x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4
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Re: x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 06:53
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trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4



\(z^2 - y^2 - x^2=(x+2)^2-(x+1)^2-x^2=x^2+4x+4-x^2-2x-1-x^2=2x-x^2+3=x(2-x)+3\)
let us see if the choices can fit in this equation..

A. -12.........\(x(2-x)+3=-12.....x(2-x)=-15 = -(3*5).. x = 5\) YES
B. -6.........\(x(2-x)+3=-6.....x(2-x)=-9\) x(2-x)=-{x(x-2)} so a multiple of two numbers with difference 2. can we write 9 as product of two such numbers..NO
C. 0.........\(x(2-x)+3=0.....x(2-x)=-3 = -(3*1).. x = 3\) YES
D. 3.........\(x(2-x)+3=3.....x(2-x)=0 = -(2*0).. x = 2\) YES
E. 4.........\(x(2-x)+3=4.....x(2-x)=1 = -(1*(-1)).. x = 1\) YES

B
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x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 06:57
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trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4


Another method to solve is going by process of elimination(substituting values for x,y,z s.t x<y<z)

A. -12 is possible for consecutive integers -3,-2, and -1
C. 0 is possible for consecutive integers -1,0, and 1
D. 3 is possible for consecutive integers 0,1, and 2
E. 4 is possible for consecutive integers 1,2, and 3

Therefore, Option B(-6) cannot be the value of \(z^2 - y^2 - x^2\)
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x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 13:25
Let x be first integer
y = x + 1
z = x + 2

So z^2 - y^2 - x^2 = x^2 +4x + 4 -(x^2 +2x + 1) - x^2

This would be = 2x + 3 - x^2
2x - x^2
X (2 - x ) + 3

Now if we put in values for x

X = 0 then the equation = 3 possible
X = 1 then the equation = 4 possible
X = 2 then the equation = 3 possible
X= 3 then the equation = 0 possible
X = 4 then the equation = - 5 possible
X = 5 then the equation = -12 possible


Answer choice B

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Re: x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 13:51
chetan2u wrote:
trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4



\(z^2 - y^2 - x^2=(x+2)^2-(x+1)^2-x^2=x^2+4x+4-x^2-2x-1-x^2=2x-x^2+3=x(2-x)+3\)
let us see if the choices can fit in this equation..

A. -12.........\(x(2-x)+3=-12.....x(2-x)=-15 = -(3*5).. x = 5\) YES
B. -6.........\(x(2-x)+3=-6.....x(2-x)=-9\) x(2-x)=-{x(x-2)} so a multiple of two numbers with difference 2. can we write 9 as product of two such numbers..NO
C. 0.........\(x(2-x)+3=0.....x(2-x)=-3 = -(3*1).. x = 3\) YES
D. 3.........\(x(2-x)+3=3.....x(2-x)=0 = -(2*0).. x = 2\) YES
E. 4.........\(x(2-x)+3=4.....x(2-x)=1 = -(1*(-1)).. x = 1\) YES

B



hello chetan2u i didnt get how did you get from this \(z^2 - y^2 - x^2\) you got this \((x+2)^2-(x+1)^2-x^2\)

I didnt get why only x`s i see whereas there is also \(z\) and \(y\) ? and where did you get +2 and +1 ? ;?

pls explain
thanks!
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Re: x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 14:04
1
dave13 wrote:
chetan2u wrote:
trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4



\(z^2 - y^2 - x^2=(x+2)^2-(x+1)^2-x^2=x^2+4x+4-x^2-2x-1-x^2=2x-x^2+3=x(2-x)+3\)
let us see if the choices can fit in this equation..

A. -12.........\(x(2-x)+3=-12.....x(2-x)=-15 = -(3*5).. x = 5\) YES
B. -6.........\(x(2-x)+3=-6.....x(2-x)=-9\) x(2-x)=-{x(x-2)} so a multiple of two numbers with difference 2. can we write 9 as product of two such numbers..NO
C. 0.........\(x(2-x)+3=0.....x(2-x)=-3 = -(3*1).. x = 3\) YES
D. 3.........\(x(2-x)+3=3.....x(2-x)=0 = -(2*0).. x = 2\) YES
E. 4.........\(x(2-x)+3=4.....x(2-x)=1 = -(1*(-1)).. x = 1\) YES

B



hello chetan2u i didnt get how did you get from this \(z^2 - y^2 - x^2\) you got this \((x+2)^2-(x+1)^2-x^2\)

I didnt get why only x`s i see whereas there is also \(z\) and \(y\) ? and where did you get +2 and +1 ? ;?

pls explain
thanks!


Hi dave I’ll give my self the liberty to answer your question.

It says x,y,z are consecutive integers and (x<y<z)

If x is the least of these 3 consecutive integers

Then y = x + 1
And z = x + 2

He just changed the variables in a way to make it simpler to deal with.

I hope this clarifies your doubt.

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x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 02 Oct 2018, 14:06
pushpitkc wrote:
trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4


Another method to solve is going by process of elimination(substituting values for x,y,z s.t x<y<z)

A. -12 is possible for consecutive integers -3,-2, and -1
C. 0 is possible for consecutive integers -1,0, and 1
D. 3 is possible for consecutive integers 0,1, and 2
E. 4 is possible for consecutive integers 1,2, and 3

Therefore, Option B(-6) cannot be the value of \(z^2 - y^2 - x^2\)


hey pushpitkc
Why do you pick negative numbers ? :? when squared negative number turns positive.
thanks

may be you know :) Salsanousi
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Re: x,y,z are consecutive integers (x<y<z). Which of the following  [#permalink]

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New post 03 Oct 2018, 00:10
dave13 wrote:
pushpitkc wrote:
trankimphuong wrote:
x,y,z are consecutive integers (x<y<z). Which of the following cannot be the value of \(z^2 - y^2 - x^2?\)

A. -12
B. -6
C. 0
D. 3
E. 4


Another method to solve is going by process of elimination(substituting values for x,y,z s.t x<y<z)

A. -12 is possible for consecutive integers -3,-2, and -1
C. 0 is possible for consecutive integers -1,0, and 1
D. 3 is possible for consecutive integers 0,1, and 2
E. 4 is possible for consecutive integers 1,2, and 3

Therefore, Option B(-6) cannot be the value of \(z^2 - y^2 - x^2\)


hey pushpitkc
Why do you pick negative numbers ? :? when squared negative number turns positive.
thanks

may be you know :) Salsanousi


Hey dave13

The reason I used negative numbers is that I needed a negative answer.
That was possible only if the magnitude of x was greater than y and y<z.

Hope that clears your confusion
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Re: x,y,z are consecutive integers (x<y<z). Which of the following &nbs [#permalink] 03 Oct 2018, 00:10
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