若tan(A+B)=2/5,tan(A-π/4）=1/4,则tan（B+π/4）等于多少?
问题描述：
若tan(A+B)=2/5,tan(A-π/4）=1/4,则tan（B+π/4）等于多少?
答
解:tan[A+(π/4)]=tan{(A+B)-[B-(π/4)]}
tan{(A+B)-[B-(π/4)]}
={tan{(A+B)-tan[B-(π/4)]}/{1+〈tan{(A+B)×tan[B-(π/4)]〉}
=[(2/5)-(1/4)]/[1+(2/5)×(1/4)]
=(3/20)/(22/20)
=3/22
答
arctan(1/4)+排/4=56.25
arctan(2/5)-B=12.69-B=56.25
B=43.56
tan(43.56+排/4)=39.78