LHS= cos11+sin11/cos11-sin11

divide both numerator and denominator by cos11

= 1+tan11/1- 1tan11

since tan 45=1 now we wil subtitute this value of 1 here in numerator

=tan45+tan11/1-tan45tan11 (since it is the formula for tan (a+b)so)

=tan(45+11)

=tan56