Question

tan {π/4 + a} tan {3π/4+a} =-1​

Answer 1

please see the attachment

Answer 2

$\tan = ( \frac{ \pi}{4} + a) \times \tan( \frac{3 \pi + A}{4} )$

$using \: tangent \: sum \: of \: angle \: formula \ratio -$

$tan(A+B) = \frac{ \tan A+ \tan B}{1 - \tan A \times \tan B }$

$in \: conjuction \: with \ratio$

$\tan( \frac{ \tan \pi }{4} ) = 1 \: and \: \tan( \frac{ \tan 3\pi }{4} ) = - 1$

$now$

$\tan( \frac{\pi}{4} + A) \times \tan( \frac{3 \pi }{4} + A)$

$= \frac{ \tan (\frac{ \pi }{4} ) + \tan A}{1 - \tan( \frac{ \pi }{4}) \times \tan A }$

$= > \frac{ \tan (\frac{3 \pi }{4} ) + \tan A}{1 - \tan( \frac{ 3\pi }{4}) \times \tan A }$

$= \frac{1 + \tan A }{1 - \tan A} \times \frac{ - 1 + \tan A }{1 + \tan A}$

$= \frac{ - 1 + \tan A }{1 - \tan A} \times \frac{ 1 - \tan A }{1 + \tan A}$

$\boxed{= - 1}$

HENCE, R.H.S = L.H.S