Question

(cos64°cos4°+ cos86°cos26°)/(cos71°cos41° + cos49°cos19° ) = -1

Answer 1

(сos(90-26)*cos4+cos(90-4)*cos26)/(cos(90-19)*cos41+cos(60-41)*cos19)=
=(sin26cos4+sin4*cos26)/(sin19*cos41+sin41cos19)=
=sin(26+4)/sin(19+41)=sin30:sin60=1/2:√3/2=1/√3