cosa-sina=-√5/5 sina=√5/5+cosacos^2a+sin^2a=12cos^2a+2√5cosa/5-4/5=0cos^2a+√5cosa/5-2/5=0cosa=√5/5或cosa=-2√5/5 0＜a＜π/2 cosa>0cosa=√5/5sina=2√5/5tana=2(2cosasina-cosa+1)/(1-tana)=(4/5-√5/5...