tan(π/4-a)tan(π/4+a)+tan(2π-a)*tan(3π/4+a)
=cot(π/4+a)tan(π/4+a)+(-tana)*(tana-1)/(tana+1)
=1-(tan²a-tana)/(tana+1)
=(-tan²a+2tana+1)/(tana+1)
tan(π/4-a)tan(π/4+a)+tan(2π-a)*tan(3π/4+a)
=cot(π/4+a)tan(π/4+a)+(-tana)*(tana-1)/(tana+1)
=1-(tan²a-tana)/(tana+1)
=(-tan²a+2tana+1)/(tana+1)