显然cosb>0.sin(a-b)=√10/10得cos(a-b)=±3√10/10.而cosb=cos[a-(a-b)]=cosacos(a-b)+sinasin(a-b)=√5/5*(±3√10/10)+2√5/5*√10/10=(2±3)√50/50显然只能取加号,否则为负值.于是cosb=(2+3)√50/50=√2/2,b=45...