Prove that: `sin(pi/10) sin((13pi)/10)=-1/4`

sin(pi/10)sin((3pi)/10)=

Prove that 4sin(pi/10) sin((13pi)/10)=-1

Prove that: sin(pi/10)+sin((13pi)/10)=-1/2

Prove that: sin(9pi)/(10) + sin(13pi)/(10)=-1/2

sinpi/10+sin(13pi)/(10)=?

Prove that: sin((pi)/(10))sin((13 pi)/(10))=-(1)/(4)

sin((pi)/(10))sin((3pi)/(10))=?

Prove that: (sin pi)/(10)+(sin(13 pi))/(10)=-(1)/(2)

Prove that: sin(pi/10). cos(pi/5)=1/4

Prove that: sin(pi/14)sin((3pi)/14)sin((5pi)/14)sin((7pi)/14)sin((9pi)/14)sin((11pi)/14)sin((13pi)/14)=1/(64)