Using cos addition formula: use x for theta cos(x+π/6)=cosx*cos(π/6)-sinx*sin(π/6) sinx=1/4 cosx=√15/4 cos(π/6)=√3/2 sin(π/6)=1/2 cos(x+π/6)=(√15/4*√3/2)-(1/4*1/2) cos(x+π/6)=(√45/8)-(1/8 ) cos(x+π/6)=(√45-1)/8)
In this situation you would have to use ratios to figure it out. AD over EH or 24/16 that would be equal to 1.5 This would show that BC over GF is also equal to 1.5. 6/4 is equal to 1.5. Side length BC is 6
. +12 on both sides to get 
. Divide by -8 to get 