`A+B+C=180^@=>cos2A+cos2B+cos2C=`

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)

In a /_ABC,sin^(4)A+sin^(4)B+sin^(4)C=(3)/(2)+2cos A cos B cos C+(1)/(2)cos2A cos2B cos2C

If A + B + C =180^@ , prove that : cos^2 A+ cos^2 B+cos^2 C=1-2 cos A cos B cosC .

If A+B+C=180^@ , then prove that cos2A + cos2B +cos2C=-1-4cosA cosB cosC .

If A+B+C=180^@ , then prove that cos^2 A + cos^2 B +cos^2 C=1-2cosA cosB cosC .

If A + B + C =180^@ , prove that : cos (-A+B +C)+cos(A-B+C)+ cos (A +B-C)=1+ 4cos A cos B cos C .

If A+B+C=180^(@) then cos A+cos B-cosC=

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

If A+ B+C= 180^(@) " then " cos 2A+ cos 2B + cos 2C+ 1=