Question
If y = tan−1√(1+sinx1−sinx),π2<x<π, then dydx equals
Answer: Option A
:
A
y=tan−1
⎷(1−cos(π2+x)1+cos(π2+x))=tan−1∣∣tan(π4+x2)∣∣⋯)(i)
Now,π2<x<π
∴π4<x2<π2
orπ2<π4+x2<3π4
∴∣∣tan(π4+x2)∣∣=−tan(π4+x2)(∴insecondquadrant)
=tan{π−(π4+x2)}
FromEq.(i),
y=tan−1tan{π−(π4+x2)}
=π−(π4+x2)
=3π4−x2
(∵principalvalueoftan−1xin−π2toπ2)
∴dydx=−12
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:
A
y=tan−1
⎷(1−cos(π2+x)1+cos(π2+x))=tan−1∣∣tan(π4+x2)∣∣⋯)(i)
Now,π2<x<π
∴π4<x2<π2
orπ2<π4+x2<3π4
∴∣∣tan(π4+x2)∣∣=−tan(π4+x2)(∴insecondquadrant)
=tan{π−(π4+x2)}
FromEq.(i),
y=tan−1tan{π−(π4+x2)}
=π−(π4+x2)
=3π4−x2
(∵principalvalueoftan−1xin−π2toπ2)
∴dydx=−12
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