... = 5tanx 2(1+tan2x) tan3x tan2x = 5tanx tan2x tan3x + tan2x 5tanx + = t t = tanx ta c phng trỡnh t = t3 + t2 5t +3 = (t 1)(t2 + 2t 3) = t = Vi t = 1, phng trỡnh tanx = cú nghim x ... cho Trang Giỏo ỏn t chn nõng cao 11 Bi 5: Gii phng trỡnh sin2x(tanx 1) = cosx(5sinx cosx) Gii: iu kin ca phng trỡnh l cosx Chia hai v ca phng trỡnh cho cos2x ta c: tan2x (tanx 1) = 5tanx ... cos2x, ta c: tan2x - tan x + =0 Trang Giỏo ỏn t chn nõng cao 11 + k v x = arctan + k, k Vy phng trỡnh ó cho cú cỏc nghim Gii phng trỡnh, ta c: x = x= + k , x = + k v x = arctan + k, k 3...