8ahil
幼苗
共回答了15个问题采纳率:86.7% 举报
(cosa-sina)^2=cos^2 a+sin^2 a-2sinacosa=1-2*(-12/25)=49/25即cosa-sina=±7/5
sina=(k+1)/(k-3);cosa=(k-1)/(k-3)由sin^2 a+cos^2 a=1则[(k+1)/(k-3)]^2+[(k-1)/(k-3)]^2=1得出k=1或k=-7 ,则sina=1,cosa=0或sina=3/5,cosa=4/5
由于cosa为分母,故cosa≠0,则tana-1/tana+1=sina/cosa-cosa/sina+1=(sin^2a -cos^2 a)/sinacosa +1=5/12
1年前
3