NIMCET 2015 — Mathematics PYQ
NIMCET | Mathematics | 2015If 0 < x < \pi and cosx+sinx=21, then the value of tanx is:
Choose the correct answer:
- A.
34−7
- B.
3−4+7
(Correct Answer) - C.
41+7
- D.
41−7
3−4+7
Explanation
cosx+sinx=21
(cosx+sinx)2=(21)2
cos2x+sin2x+2sinxcosx=41
1+sin2x=41
sin2x=41−1=−43
1+tan2x2tanx=−43
8tanx=−3−3tan2x
3tan2x+8tanx+3=0
tanx=2(3)−8±82−4(3)(3)
tanx=6−8±64−36
tanx=6−8±28
tanx=6−8±27
tanx=3−4±7
Since 0 < x < \pi and \sin 2x < 0, x is in the second quadrant.
In second quadrant, tanx is negative.
From options:
tanx=3−4+7
Correct Option: (b)
Explanation
cosx+sinx=21
(cosx+sinx)2=(21)2
cos2x+sin2x+2sinxcosx=41
1+sin2x=41
sin2x=41−1=−43
1+tan2x2tanx=−43
8tanx=−3−3tan2x
3tan2x+8tanx+3=0
tanx=2(3)−8±82−4(3)(3)
tanx=6−8±64−36
tanx=6−8±28
tanx=6−8±27
tanx=3−4±7
Since 0 < x < \pi and \sin 2x < 0, x is in the second quadrant.
In second quadrant, tanx is negative.
From options:
tanx=3−4+7
Correct Option: (b)