Question

quickly answer this question

Answer 1

bro 18 no. main sec-tan/sec-tan se multiple karo aur answer milega
19. number main cosec-cot/cosec-cot se multiple karo

Answer 2

$18. \: \: l.h.s. \\ \\ = \frac{1}{ \sec( \alpha ) + \tan( \alpha ) } \\ \\ \frac{1 \times ( \sec( \alpha ) - \tan( \alpha ) )}{( \sec( \alpha ) + \tan( \alpha ) )( \sec( \alpha ) - \tan( \alpha ) )} \\ \\ \frac{ \sec( \alpha ) - \tan( \alpha ) }{ \sec {}^{2} ( \alpha ) - \tan {}^{2} ( \alpha ) } \\ \\ = \frac{ \sec( \alpha ) - \tan( \alpha ) }{1} \\ \\ = \sec( \alpha ) - \tan( \alpha ) = r.h.s.$
proved

hope it helps....