估计你的输入有误吧,4搁错地方了.
是tan(A+B)=2/5,tan(B-π/4)=1/4
tan(A+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)]
分子分母同时乘以20
=(8-5)/(20+2)
=3/22没有啊啊？那为啥是2/54？题目是这样喵怎么知道tan(A+B)=2/54=1/27,tan(B-π)=1/4,即tanB=1/4∴ tanA=tan[(A+B)-B]=[tan(A+B)-tanB]/[1+tan(A+B)tanB]=[(1/27)-(1/4)]/[1+(1/27)*(1/4)]=-23/109 tan(A+π/4)=[tanA+tan(π/4)]/[1-tanAtan(π/4)]=(tanA+1)/(1-tanA)=(-23/109+1)/(1+23/109)=86/132=43/66