If `a= b cos ""(2pi)/(3) = c cos ""(4pi)/(3),` then the value of `(ab+ bc +ca)` is-

If a = b cos "" ( 2 pi)/ (3) = c cos "" (4 pi)/( 3) , then write the value of ab + bc + ca

If a=b cos((2pi)/3)= c cos((4pi)/3), then write the value of a b+b c+c a

If a=b(cos(2 pi))/(3)=(cos(4 pi))/(3), then write the value o ab+bc+ca

If asintheta = bsin(theta+(2pi)/(3)) = csin(theta+(4pi)/(3)) , then the value of ab+bc+ca is ___________.

Let a, b,c are respectively the sines and p, q, r are respectively the consines of alpha, alpha+(2pi)/(3) and alpha+(4pi)/(3) , then : Q. The value of (ab+bc+ca) is :

Let a, b,c are respectively the sines and p, q, r are respectively the consines of alpha, alpha+(2pi)/(3) and alpha+(4pi)/(3) , then : Q. The value of (ab+bc+ca) is :

If x cos theta = y cos (theta + (2pi)/(3)) = z cos (theta + (4pi)/(3)) , find the value of xy + yz + zx

If a cos theta = b cos ( theta+(2 pi)/3)= c cos ( theta+ (4pi)/3),"prove that" ab+bc+ca=0.