[(1)/(2sin10^(@))-2sin70^(@)-4 pi(pi)/(6)1],[[" (A) "-2," (B) "0],[" (C) "(sqrt(3))/(2)," (D) "1]]

(1-4 sin 10^(@) sin70^(@))/(2 sin 10^(@))=

sin ^(2) " (pi)/(6) + cos ^(2) "" (pi)/(3) - tan ^(2) " (pi)/(4) =- 1/2

sin ^(2) " (pi)/(6) + cos ^(2) "" (pi)/(3) - tan ^(2) " (pi)/(4) =- 1/2

(1+sin2A)/(1-sin2A)=tan^(2)((pi)/(4)+A)

tan^(-1)[sin(-pi/2)]=pi/4 .

sin^(2) (pi/6)+cos^(2) (pi/3)-tan^(2) (pi/4)=-1/2

sin(pi/6-sin^(-1)(-1/2))=?

Show that : "sin" 2(pi)/(7)+ "sin"(4pi)/(7)-"sin" (6pi)/(7) =4 "sin" (pi)/(7) "sin" (2pi)/(7) "sin" (3pi)/(7)

sin(pi/10)sin((3pi)/10)= ............ A) 1/2 B) (-1)/(2) C) (1)/(4) D) 1