Prove that:
`sinpi/10. cospi/5=1/4`

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

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

Prove that: 8cos^3pi/9-\ 6cospi/9=1.

Prove that: i) sin(5pi)/(18) - cos(4pi)/(9) = sqrt(3)sinpi/9 ii) cos(3pi)/4+A-cos((3pi)/(4)-A)=-sqrt(2)sinA

Prove that: i) sin(5pi)/(18) - cos(4pi)/(9) = sqrt(3)sinpi/9 ii) cos(3pi)/4+A-cos((3pi)/(4)-A)=-sqrt(2)sinA

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

Prove that: cospi/10-sinpi/10=sqrt(2)sin(3pi)/(20)

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

Prove that: 108sinpi/(18)-144sin^3pi/(18)=18

Prove that: sinpi/7+sin(2pi)/(7) + sin(8pi)/7 + sin(9pi)/7=0