sin(x+7π/6)=sin(x+π/6+π)=-1/4
sin(5π/6-x）=:sin(x+π/6-π)=-1/4
cos^2 (5π/6-x）=1-1/16=15/16
sin(x+7π/6)+cos^2 (5π/6-x)=11/16