((sin^2(173)-cos^2(187))/sin76

((sin^2(173)-cos^2(187))/sin76=

(sin^2(180-7) -cos^2(180+7))/sin76=

(sin^2(7)-cos^2(7))/sin(90-14)=

-(cos^2(7)-sin^2(7))/cos(14)=

-cos(2*7)/cos(14)=-cos(14)/cos(14)=-1