Prove that
` cos (pi + theta) = - cos theta`

If n is an integer,prove that cos(n pi+theta)=(-1)^(n)cos theta

Prove that (cos (pi-theta).cot(pi/2 +theta).cos(-theta))/(tan(pi+theta).tan((3pi)/(2)+theta).sin(2pi-theta))=cos theta

If theta = pi/7 prove that cos theta* cos 2theta * cos 3theta = 1/8

If 13 theta =pi , " prove that " cos theta cos 2theta cos3 theta cos4theta cos5 theta cos6 theta =1/2^(6)

Prove that cos theta + cos ((2pi)/(3)- theta)+ cos ((2pi)/(3)+ theta)=0

Prove that cos theta + cos[(2pi)/3 + theta] + cos [(4pi)/(3) + theta] = 0 .

If theta=(pi)/(7), prove that cos theta cos2 theta cos3 theta=(1)/(2^(3))

If theta=(pi)/(9), prove that cos theta cos2 theta cos3 theta cos4 theta=(1)/(16)

Prove that: (cos(2 pi+theta)csc(2 pi+theta)tan(pi/2+theta))/(sec(pi/2+theta)cos theta cot(pi+theta))=1

Prove that : cos (pi/4- theta)cos (pi/4-phi)-sin(pi/4-theta) sin (pi/4-phi)= sin (theta+phi) .