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3.Trigonometrical Ratios, Functions and Identities
easy
यदि $\sin \theta + \cos \theta = m$ तथा $\sec \theta + {\rm{cosec}}\theta = n$, तो $n(m + 1)(m - 1) = $
A
$m$
B
$n$
C
$2m$
D
$2n$
Solution
(c) $n({m^2} – 1) = (\sec \theta + {\rm{cosec}}\theta ).2\sin \theta \cos \theta $ ($\because$ ${m^2} = 1 + 2\sin \theta \cos \theta $)
$ = \frac{{\sin \theta + \cos \theta }}{{\sin \theta .\cos \theta }}.2\sin \theta \cos \theta = 2m$.
Standard 11
Mathematics
