This is not an expression, but an equation which is false, because it would mean that sin110/cos110=sin80/cos80; tan110=tan80 or 110=80, which cannot be true. Therefore, replace equals by minus and we have an expression which can be rewritten: sin(110-80)=sin30=1/2=cos60. Tan30=sqrt(3)/3 and tan60=1/tan30=sqrt(3).