highfive287 wrote:My explaination is:
(1) -1/(k-1) > 0 . If you times (-1), you will get 1 / (k-1) < 0 . Because k can't be 0, K has to be negative in order to make 1/ (k -1) < 0.
(2) -1/ (k +1) > 0. If you times (-1), you will also get 1/ (k+1) < 0. K has to be negative to make the equation is valid.
The answer is D.
highfive287, you misunderstood a hyphen after the equation number to mean a negative sign. Viz. 1- and 2- ...
So, its not -1/(k-1), its 1/(k-1)
Also, its not -1/(k+1), its 1/(k+1)
Here is my thinking:
for 1/k to be greater than 0, i.e. for 1/k > 0 to be true, k must satisfy this range:
0 < k <= 1 .......... (eq1)
That means, that k should be a fraction, less than 1 but still positive.
(1) 1/(k-1) > 0
For this to be true, applying the same logic as above
= 0 < (k-1) <= 1 must be true
= 1 < k <= 2 must be true
this violates the above (eq1) with certainty and hence is SUFFICIENT to answer the original question. The answer would be NO, 1/k is not greater than 0, but we are not interested in the answer.
(2) 1/(k+1) > 0
For this to be true, applying the same logic as above
= 0 < (k+1) <= 1 must be true
= -1 < k <= 0 must be true
this violates the above (eq1) with certainty and hence is SUFFICIENT to answer the original question. The answer would be NO, 1/k is not greater than 0, but we are not interested in the answer.
Final answer would be (D), each statement alone is sufficient.
