cos(9/4π) + 1/tan(-7π/6) + sin(-π) + 1/tan(-5π/6)=cos(2π+1/4π) + 1/tan(-2π+5/6π) + sin(-π) + 1/tan(-2π+7/6π)=cos(1/4π) + 1/tan(5/6π) + sin(-π) + 1/tan(π+1/6π)=√2/2 +1/tan(π-1/6π) + ...