`cosA/(bcosC + c cosB) + cosB/(c cosA + acosC) + cosC/(acosB + bcosA)` =

In a triangle ABC , if a,b,c are the sides opposite to angles A , B , C respectively, then the value of |{:(bcosC,a,c cosB),(c cosA,b,acosC),(acosB,c,bcosA):}| is (a) 1 (b) -1 (c) 0 (d) acosA+bcosB+c cosC

In a triangle ABC, prove that: cos^4A+cos^4B+cos^4C= 3/2 + 2 cosA cosB cosC+ 1/2 cos 2A cos2B cos2C

In any A B C ,2(bc cosA+ ca cosB+ab cosC) =

In a quadrilateral if sin(A+B)/2cos(A-B)/2+sin(c+D)/2cos(c-D)/2=2, then cosA/2cosB/2+cosA/2cosc/2+cosA/2 cosD/2+cosB/2 cosC/2+cosB/2 cosD/2+cosC/2 cosD/2=

2(bc cosA+c acosB+a bcosC)=a^2+b^2+c^2

(a+b+c)(cosA+cosB+cosC)

If A+B+C=pi , prove that : sinA cosB cosC +sinB cosC cosA + sinC cosA cosB = sinA sinB sinC .

If in a triangle A B C ,(1+cosA)/a+(1+cosB)/b+(1+cosC)/c =(k^2(1+cosA)(1+cosB)(1+cosC)/(a b c) , then k is equal to (a) 1/(2sqrt(2)R) (b) 2R (c) 1/R (d) none of these

If A+B+C=pi , prove that : (cosA)/(sinb sinC) + (cosB)/(sinC sin) + (cosC)/(sinA sinB) =2 .

(Projection Formulae) if a ,b ,c are the lengths of the sides opposite respectively to the angles A ,B ,C of a triangle A B C , show that a=bcosC+ccosB (ii) b=ccosA+acosC (iii) c=acosB+bcosA