The three most important are to bear the load of the building, anchor it against natural forces such as earthquakes, and to isolate it from ground moisture. The relative importance of these functions changes with the type of land underneath the building and the building design
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)
