tan（a+π/4）= 3/5{ tana + tan(π/4) } / { 1 - tana*tan(π/4) } = 3/5( tana + 1) / ( 1 - tana*1 ) = 3/53( 1 - tana ) = 5( tana + 1) 3 - 3tana = 5 tana + 5 8 tana = -2tana = -1/4