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value of k^2-k

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value of k^2-k

by sairamGmat » Mon Jul 19, 2010 4:31 pm
What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
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by Rahul@gurome » Mon Jul 19, 2010 4:40 pm
sairamGmat wrote:What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
(1) k - 1/k = 1 or k^2 - 1 = k or k^2 - k = 1. So, (1) is SUFFICIENT.

(2) 2k - 1 = √(5) or k = (1 + √5)/2
So, k^2 - k = [(1 + √5)/2]^2 - [(1 + √5)/2] = [1 + 5 + 2√5 - 2 - 2√5]/4 =4/4 =1
So, (2) is SUFFICIENT.

Hence, correct answer is (D).
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by singhpreet1 » Tue Jul 20, 2010 1:20 am
Rahul@gurome wrote:
sairamGmat wrote:What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
(1) k - 1/k = 1 or k^2 - 1 = k or k^2 - k = 1. So, (1) is SUFFICIENT.

(2) 2k - 1 = √(5) or k = (1 + √5)/2
So, k^2 - k = [(1 + √5)/2]^2 - [(1 + √5)/2] = [1 + 5 + 2√5 - 2 - 2√5]/4 =4/4 =1
So, (2) is SUFFICIENT.

Hence, correct answer is (D).
Hi Rahul,

i fail to understand how could k-1/k=1 could be translated into k^2-1=k would it not be k-1=k;
also if k=1, then k-1/k would interpret into 1-1/1=0 not 1? where i am missing the point?

Preet
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by aloneontheedge » Tue Jul 20, 2010 1:37 am
singhpreet1 wrote:
Rahul@gurome wrote:
sairamGmat wrote:What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
(1) k - 1/k = 1 or k^2 - 1 = k or k^2 - k = 1. So, (1) is SUFFICIENT.

(2) 2k - 1 = √(5) or k = (1 + √5)/2
So, k^2 - k = [(1 + √5)/2]^2 - [(1 + √5)/2] = [1 + 5 + 2√5 - 2 - 2√5]/4 =4/4 =1
So, (2) is SUFFICIENT.

Hence, correct answer is (D).
Hi Rahul,

i fail to understand how could k-1/k=1 could be translated into k^2-1=k would it not be k-1=k;
also if k=1, then k-1/k would interpret into 1-1/1=0 not 1? where i am missing the point?

Preet
Preet,
k - 1/k =1
k^2-1/K =1 or k^2-1=k
k^2-k = 1
hope its clear
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by aloneontheedge » Tue Jul 20, 2010 1:37 am
singhpreet1 wrote:
Rahul@gurome wrote:
sairamGmat wrote:What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
(1) k - 1/k = 1 or k^2 - 1 = k or k^2 - k = 1. So, (1) is SUFFICIENT.

(2) 2k - 1 = √(5) or k = (1 + √5)/2
So, k^2 - k = [(1 + √5)/2]^2 - [(1 + √5)/2] = [1 + 5 + 2√5 - 2 - 2√5]/4 =4/4 =1
So, (2) is SUFFICIENT.

Hence, correct answer is (D).
Hi Rahul,

i fail to understand how could k-1/k=1 could be translated into k^2-1=k would it not be k-1=k;
also if k=1, then k-1/k would interpret into 1-1/1=0 not 1? where i am missing the point?

Preet
Preet,
k - 1/k =1
k^2-1/K =1 or k^2-1=k
k^2-k = 1
hope its clear
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by singhpreet1 » Tue Jul 20, 2010 1:53 am
aloneontheedge wrote:
singhpreet1 wrote:
Rahul@gurome wrote:
sairamGmat wrote:What is the value of k^2-k?
(1) The value of k - 1/k is 1.
(2) The value of 2k -1 is squr(5).

OA answer is D

But not sure why is it not just B. Because using (2) we get k = [1+sqrt(5)]/2. This is sufficient to be substituted in k^2-k right?

With (1), we get an equation k^2-k-1=0. This will give us two roots. So, not sure why the answer is not B, but OA
(1) k - 1/k = 1 or k^2 - 1 = k or k^2 - k = 1. So, (1) is SUFFICIENT.

(2) 2k - 1 = √(5) or k = (1 + √5)/2
So, k^2 - k = [(1 + √5)/2]^2 - [(1 + √5)/2] = [1 + 5 + 2√5 - 2 - 2√5]/4 =4/4 =1
So, (2) is SUFFICIENT.

Hence, correct answer is (D).
Hi Rahul,

i fail to understand how could k-1/k=1 could be translated into k^2-1=k would it not be k-1=k;
also if k=1, then k-1/k would interpret into 1-1/1=0 not 1? where i am missing the point?

Preet
Preet,
k - 1/k =1
k^2-1/K =1 or k^2-1=k
k^2-k = 1
hope its clear
you have only paraphrased what Rahul and i have written...it is still a mountain for me!

Preet
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by blaster » Tue Jul 20, 2010 4:08 am
agree with singhpreet1
it's not clear.

k - 1/k =1
k^2-1/K =1 or k^2-1=k

the red part ,which is not clear.
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by Rahul@gurome » Tue Jul 20, 2010 4:21 am
blaster wrote:agree with singhpreet1
it's not clear.

k - 1/k =1
k^2-1/K =1 or k^2-1=k

the red part ,which is not clear.
Please see the attachment, does that help?
Attachments
Expression.doc
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by singhpreet1 » Tue Jul 20, 2010 7:34 am
Rahul@gurome wrote:
blaster wrote:agree with singhpreet1
it's not clear.

k - 1/k =1
k^2-1/K =1 or k^2-1=k

the red part ,which is not clear.
Please see the attachment, does that help?
ohh my GOD! bless me!

so sorry to give Rahul and everyone so much trouble..i think i have these phases where i cant read right!!

i was reading it as k-1 divided by k=1, whereas the question was k minus 1/k=1.

sorry again and thank u for your patience!

Preet
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by blaster » Tue Jul 20, 2010 11:57 am
Rahul@gurome wrote:
blaster wrote:agree with singhpreet1
it's not clear.

k - 1/k =1
k^2-1/K =1 or k^2-1=k

the red part ,which is not clear.
Please see the attachment, does that help?
thank you. i thought that it must be like this (k-1)/k=1. my mistake.
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by Rahul@gurome » Tue Jul 20, 2010 8:11 pm
singhpreet1 wrote:
ohh my GOD! bless me!

so sorry to give Rahul and everyone so much trouble..i think i have these phases where i cant read right!!

i was reading it as k-1 divided by k=1, whereas the question was k minus 1/k=1.

sorry again and thank u for your patience!

Preet
Preet, it happens sometimes. You are welcome :-)
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