Question

Cos(85o)+sin(125o)−cos(25o) . помогите решить

Answer 1

$cos(85^\circ)-cos(25^\circ)=-2sin(55^\circ)sin(30^\circ)=-sin(55^\circ)\\sin(125^\circ)=sin(180^\circ-55^\circ)=sin(55^\circ)\\\\sin(55^\circ)-sin(55^\circ)=0$