Prove that `a cos A + b cos B + c cos C = 4 R sin A sin B sin C.`

If A + B + C = 180^@ , then prove that sin 2 A+ sin 2B + sin 2C = 4 sin A sin B sin C

If A= 30° and B = 60°, verify that cos (A+ B) = cos A cos B - sin A sin B.

If cos(A-B)=3/5a n d\ t a n AtanB=2, t h e n cos A\ cosB=1/5 b. cosA\ cos B=\ -1/5 c. sin A\ sin B=\ -1/5 d. sin A\ sin B=\ -1/5

y = cos x + C : y' + sin x = 0

Given that sin (A+ B) = sin A cos B + cos A sin B , find the value of sin 75° .

For any "Delta"A B C the value of determinant |sin^2\ \ A cot A1sin^2B cot B1sin^2\ \ C cot C1| is equal to- s in A s in B s in C b. 1 c. 0 d. s in A+s in B+s in C

In a right angle triangle ABC, right angle is at B ,If tan A=sqrt(3) , then find the value of (i) sin A cos C+ cos A sin C " "(ii) cos A cos C -sin A sin C

If a = cos theta + isin theta , b = cosphi + isinphi , c = cos psi + i sin psi and a/b+b/c+c/a=2 then sin(theta-phi)+sin(phi-psi)+sin(psi-theta) equals

If DeltaABC is a right angle triangle then prove that cos^(2)A+cos^(2)B+cos^(2)C=1iffsin^(2)A+sin^(2)B+sin^(2)C=2

Using the fact that sin (A +B) = sin A.cos B+ cos A sin B and the differentiation, obtain the sum formula for cosines.