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3.Trigonometrical Ratios, Functions and Identities
medium
$k$ के किस मान के लिए ${(\cos x + \sin x)^2} + k\,\sin x\cos x - 1 = 0$ एक सर्वसमिका होगी
A
$-1$
B
$-2$
C
$0$
D
$1$
Solution
(b) दिया है , ${(\cos x + \sin x)^2} + k\sin x\cos x – 1 = 0,\,\forall \,x$
==> ${\cos ^2}x + {\sin ^2}x + 2\cos x\sin x + k\sin x\cos x – 1 = 0,\,\forall \,x$
==> $(k + 2)\cos x\sin x = 0,\,\forall \,x$ ==> $k + 2 = 0$ ==> $k = – 2$.
Standard 11
Mathematics