NIMCET 2011 — Mathematics PYQ
NIMCET | Mathematics | 2011If sinx,cosx and tanx are in GP, then cot6x−cot2x will be equal to:
Choose the correct answer:
- A.
2
- B.
-1
- C.
1
(Correct Answer) - D.
0
1
Explanation
1. Apply GP Condition:
Since the terms are in Geometric Progression:
cos2x=sinx⋅tanx
cos2x=sinx⋅cosxsinx
cos3x=sin2x
2. Express in terms of cotx:
Divide both sides by sin3x:
sin3xcos3x=sin3xsin2x
cot3x=sinx1
3. Square both sides:
cot6x=sin2x1
Using the identity sin2x1=csc2x:
cot6x=1+cot2x
4. Find the required value:
cot6x−cot2x=1
Correct Option: (c)
Explanation
1. Apply GP Condition:
Since the terms are in Geometric Progression:
cos2x=sinx⋅tanx
cos2x=sinx⋅cosxsinx
cos3x=sin2x
2. Express in terms of cotx:
Divide both sides by sin3x:
sin3xcos3x=sin3xsin2x
cot3x=sinx1
3. Square both sides:
cot6x=sin2x1
Using the identity sin2x1=csc2x:
cot6x=1+cot2x
4. Find the required value:
cot6x−cot2x=1
Correct Option: (c)
