1.

If \[\theta ={{\tan }^{-1}}a,\varphi ={{\tan }^{-1}}b\] and \[ab=-1,\] then \[\theta -\varphi =\]

A. 0
B. \[\frac{\pi }{4}\]
C. \[\frac{\pi }{2}\]
D. None of these
Answer» D. None of these


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