Question 401144
(a){{{tan A = sqrt(6)/3 = (sqrt(6)/sqrt(15))/(3/sqrt(15)) = sin A/cosA}}}
==> {{{sin A = sqrt(6)/sqrt(15) = sqrt(2)/sqrt(5) = sqrt(10)/5 = (1/5)*sqrt(10)}}}.

(b){{{cos (2A) = 1-2sin^2(A) = 1 - 2*(10/25) = 1 - 4/5 = 1/5}}}