If cos40=a, what is sin10 equal to?

Question

If cos40=a, what is sin10 equal to?, related with a .

Answer 1

Using  cos(2*theta)=2cos(theta)^2-1

     cos(80)=2cos(40)^2-1

                 =2a^2-1

 

Sin(90-80)=cos(80)=2a^2-1

 

Sin(10)=2a^2-1