3cosa-sina=19cos²a-6cosasina+sin²a=18cos²a-6cosasina+1=1cosa(4cosa-3sina)=0coaa=0或4cosa=3sinacosa=0sinacosa=04cosa=3sina(1)3cosa-sina=1(2)(1)*3-(2)*44sina=9sina-45sina=4sina=4/5cosa=3/...