解答：tana=tan[(a+π/4)-π/4]=[tan(a+π/4)-tan(π/4)]/[1+tan(a+π/4)tan(π/4)]=(3-1)/(1+3*1)=1/2
解：tan(a+π/4)=3 tanπ/4 =1[tana+tan(π/4)]/【1-tanatanπ/4】=3tana+1=3-3tanatana=1/2
