tan（a／2－π／4)=[tan(a/2)-tan(π/4)]/[1+tan(a/2)tan(π/4)]=[tan(a/2)-1]/[1+tan(a/2)]sina=3/5 ,a为第二象限角cosa = -4/5tana = -3/4又tana = 2tan(a/2)/[1-tan²(a/2)] = -3/4解得tan(a/2)=3或-1/3a为第...