设tan(a+派/4）=xtan(a+b)=(x+1/4)/(1-x/4)2/5=(4x+1)/(4-x)8-2x=20x+522x=3x=3/22tan(a+派/4)=3/22tan(派/2-a-派/4）=22/3tan(派/4-a）=22/3tan(a-派/4)=22/3sec^2(a-派/4)=(9+22^2)/9=493/9cos^2(a-派/4)=9/493cos...