1.tanπ/8+1/(tanπ/12)=2.(tan5°-1/tan5°)cos70°/(1+sin70°)这个说是什么倍角或半角公式的应用,因为刚学不怎么会啊

tan(π/12)-(1/tan(π/12)) 化简：tan(π/8)+1/tan(π/12) tan(π/8)+1/(tan(π/12))值,要过程 (1-tan^2π/12)/(tanπ/12)化简 计算 tanπ/12+1/tanπ/12 计算tanπ/12 / (1-tan^2π/12)= tan(π/12)+1/tan(π/12)=啥? tanπ/12-1/tanπ/12= (tan(5π/8)*tan(π/8))为什么等于-1 tanπ/8/(1-tan^2π/8) tanπ/8-1/tanπ/8是（tanπ/8）-〔1/（tanπ/8）〕。 三角函数算值题1-tan^2(π/8) /tan(π/8)=tan(15)/1-tan^2(15)= 这道题为什么第二步的+到了第三步变成了-1.tan(x/2+π/4)+tan(x/2-π/4)=[tan(x/2)+tan(π/4)]/[1-tan(x/2)tan(π/4)]+[tan(x/2)-tan(π/4)]/[1+tan(x/2)tan(π/4)]=[tan(x/2)+1]/[1-tan(x/2)]+[tan(x/2)-1]/[1+tan(x/2)]=[(tan(x/2)+1)^2-(tan(x/2)- 化简：[tan(5/4)π+tan(5/12)π]/[1-tan(5/12)π] 化简：[tan（5π）/4+tan(5π)/12]/[1-tan(5π)/12] 求tan(π/8) tan(π/8)=? （tanπ/4+tanα)/(1-tanπ/4tanα)怎么解