[1-tan(π/4-A)]/[1+tan(π/4+A)]
=[tan(π/4)-tan(π/4-A)]/[1+tan(π/4)*tan(π/4+A)]
=tan(π/4-π/4/4+A)
=tan(A)
此题关键是利用1=tan(π/4)来进行转换
如果认为讲解不够清楚,