Question

tan(pi/4+a)=0.5 (1)求tana(2)求sin2a-cos^2a/1+cos2a

Answer 1

tan(π/4+a)=(tanπ/4+tana)/(1-tanπ/4tana)=(1+tana)/(1-tana)=1/2

2+2tana=1-tana

tana=-1/3

sina/cosa=tana=-1/3

cosa=-3sina

代入(sina)^2+(cosa)^2=1

所以(sina)^2=1/10

(cosa)^2=9/10

sina/cosa=-1/3