" (ii) "cos(theta)/(2)=(1)/(2)

If veca,vecb are unit vectors and theta is the angle between them, show that cos""(theta)/(2)=(1)/(2)|veca+vecb|

If cos theta=(1)/(2)(a+(1)/(a)), show that cos2 theta=(1)/(2)*(a^(2)+(1)/(a^(2)))

If theta is the angle between the unit vectors veca and vecb , then prove that cos((theta)/2)=1/2|veca+vecb|

(cos 3theta)/(2cos 2theta-1)=(1)/(2) if

(cos3theta)/(2cos2theta-1)=(1)/(2) if

Delta=|(cos""(theta)/(2),1,1),(1,cos""(theta)/(2),-cos""(theta)/(2)),(-cos""(theta)/(2),1,1)| lies in the interval

If veca and vecb are unit vectors inclined at an angle theta then prove that cos(theta/2) = 1/2|veca +vecb|