若sina-cosa=1/3,0
问题描述：
若sina-cosa=1/3,0
答
由sina-cosa=1/3
sin^2+cos^2=1
联立得：9sin^2a-2/3*sina-4=0
sina1=(1+√17)/6
sina2=(1-√17)/6(小于0，舍去)
故sina=(1+√17)/6
sin2a+cos2a
=2sinacosa+1-2sin^2a
=1+2sina(cosa-sina)
=1+2sina*(-1/3)
=1+2*[(1+√17)/6]*(-1/3)
=(8-√17)/9
答
sina-cosa=1/3两边平方(sina)^2-2sinacosa+(cosa)^2=1/9(sina)^2+(cosa)^2=1所以sin2a=2sinacosa=8/9cosa=sina-1/3带入(sina)^2+(cosa)^2=1为了方便,令x=sinax^2+(x-1/3)^2=12x^2-2x/3-8/9=09x^2-3x-4=0x=(1±√17)/...