tan(π/4+a)
=(tanπ/4+tana)/(1-tanπ/4tana)
=(1+tana)/(1-tana)
=2
1+tana=2-2tana
3tana=1
tana=1/3
1/(2sinacosa+cos²a)
=(sin²a+cos²a)/(2sinacosa+cos²a)
分子分母同时除以cos²a
=(tan²a+1)/(2tana+1)
=(1/9+1)/(2/3+1)
=2/3