+312 beta=B
sec(B)=1/(cos)
tan(B)=sin(B)/cos(B)
tan^2(B)=5-4sec(B) ......multiply by cos^2(B)
sin^2(B)=5*cos^2(B)-4cos(B)
using the identity sin^2(X)+cos^2(X)=1
sin^2(B)=1-cos^2(B)=5cos^2(B)-4*cos^2(B)........add (cos^2(B)-1)
0=6*cos^2(B)-4cos^2(B)-1.......divide by 6
0=cos^2(B)-(2/3)*cos(B)-1/6=(cos(B)-(1/3))^2-1/18......add 1/18
1/18=(cos(B)-(1/3))^2
i think you can continue from here
