Question

(8sin9 * cos9 * cos 18)/cos54

Answer 1

$frac{8sin9*cos9*cos18}{cos54}= frac{4(2sin9*cos9)*cos18}{cos54}= frac{4sin(2*9)cos18}{cos54}=\\= frac{4sin18*cos18}{cos54}= frac{2(2sin18*cos18)}{cos54}= frac{2sin(2*18)}{cos54}= frac{2sin36}{cos54}=\\= frac{2sin(90-54)}{cos54}= frac{2cos54}{cos54}=2$