" 17."A+B+C=90^(@)rArr cos2A+cos2B+cos2C=

A + B + C = 180 ^ (@) rArr cos2A + cos2B + cos2C =

A+B+C=180^(@),cos2A+cos2B+cos2C=

If A+B+C=270^(@) then cos2A+cos2B+cos2C=

A+B+C=90'rArr cos^(2)A+cos^(2)B+cos^(2)C=

If A+B+C=90^(@) then (cos2A+cos2B+cos2C-1)/(sin A sin B sin C)=

If A+B+C=180^(@) then cos2A+cos2B+cos2C=1-4cos A cos B cos C 2.If A+B+C=0 then cos A+cos B+cos C=-1+4(cos A)/(2)(cos B)/(2)(cos C)/(2)

If A+B+C=90^(@) then (cos 2A+cos 2B+cos 2C-1)/(sin A sin B sin C)=

If A+B+C=180^(@) , then (cos2A+cos2B+cos2C+1)/(cos A cos B cos C)

If A+B+C=270^(@), then cos2A+cos2B+cos2C+4sin A sin B sin C=