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).

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

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

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

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?

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?