$1+\cos 10^{\circ}+\cos 20^{\circ}+\cos 30^{\circ}=$

  • A
    $4 \sin 10^{\circ} \sin 20^{\circ} \sin 30^{\circ}$
  • B
    $4 \cos 5^{\circ} \cos 10^{\circ} \cos 15^{\circ}$
  • C
    $4 \cos 10^{\circ} \cos 20^{\circ} \cos 30^{\circ}$
  • D
    $4 \sin 5^{\circ} \sin 10^{\circ} \sin 15^{\circ}$

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सिद्ध कीजिए कि: $\sin x + \sin 3x + \sin 5x + \sin 7x = 4 \cos x \cos 2x \sin 4x$

$1 + \cos 2x + \cos 4x + \cos 6x = $

सिद्ध कीजिए कि $\cot 4x(\sin 5x + \sin 3x) = \cot x(\sin 5x - \sin 3x)$

यदि $\cos (\alpha+\beta)=\frac{4}{5}$,$\sin (\alpha-\beta)=\frac{5}{13}$ और $\alpha, \beta$ का मान $0$ और $\frac{\pi}{4}$ के बीच है,तो $\tan 2 \alpha$ का मान ज्ञात कीजिए।

यदि $\sin A = \frac{4}{5}$ और $\cos B = -\frac{12}{13}$ है,जहाँ $A$ और $B$ क्रमशः प्रथम और तृतीय चतुर्थांश में स्थित हैं,तो $\cos(A + B) = $

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