[" If "cos20^(@)-sin20^(@)=p" ,then "cos49^(@)" is equal to "],[[" (a) "p^(2)sqrt(2-p^(2))," (b) "(p sqrt(2)-p^(2))/((d))(sqrt(2)-p^(2))/(d-p^(2))]],[[" (c) "p+sqrt(2-p^(2))," (d) "p-sqrt(2-p^(2))]]