For each of the following expressions, use co-terminal angles and the reference angle theorem to write an equivalent expression, and then evaluate exactly. 

(a)  sin(1425)=\displaystyle {\sin{{\left({1425}^{\circ}\right)}}}=  sin(\displaystyle {\sin{{(}}}  )=\displaystyle {)}= 

(b)  cos(1095)=\displaystyle {\cos{{\left({1095}^{\circ}\right)}}}= cos(\displaystyle {\cos{{(}}} )=\displaystyle {)}= 

(c)  tan(1815)=\displaystyle {\tan{{\left({1815}^{\circ}\right)}}}=  tan(\displaystyle {\tan{{(}}}  )=\displaystyle {)}=