sin15+cos15=根号(sin15+cos15)^2=根号(sin^2 15+cos^2 15+2sin15*cos15)=根号(1+2sin15*cos15)=根号(1+sin30)=根号(1+cos60)=根号[1+(2cos^2 30-1)]=根号[2*cos^2 30]=根号[2*sin^2 60]=根号2*sin60...