First, let's simplify the expression step by step:
15cos x (1 + tg x tg x/2) (1 - tg^2 x) / cos 2x (1 + tg^2 x)= 15cos x (1 + sin x/ cos x * sin x/ (2cos x)) (1 - sin^2x/ cos^2x) / (2cos^2x - 1) (1 + sin^2x/ cos^2x)= 15cos x (1 + sin^2x/ 2cos^2x) (1 - sin^2x/ cos^2x) / (2cos^2x - 1) (1 + sin^2x/ cos^2x)= 15cos x (2cos^2x + sin^2x) (cos^2x - sin^2x) / (2cos^2x - 1) (cos^2x + sin^2x)= 15cos x (cos^2x + sin^2x) / (2cos^2x - 1)= 15cos x / (2cos^2x - 1)
Therefore, the simplified expression is 15cos x / (2cos^2x - 1).
First, let's simplify the expression step by step:
Recall that cos 2x = 1 - 2sin^2x = 2cos^2x - 1.15cos x (1 + tg x tg x/2) (1 - tg^2 x) / cos 2x (1 + tg^2 x)
= 15cos x (1 + sin x/ cos x * sin x/ (2cos x)) (1 - sin^2x/ cos^2x) / (2cos^2x - 1) (1 + sin^2x/ cos^2x)
= 15cos x (1 + sin^2x/ 2cos^2x) (1 - sin^2x/ cos^2x) / (2cos^2x - 1) (1 + sin^2x/ cos^2x)
= 15cos x (2cos^2x + sin^2x) (cos^2x - sin^2x) / (2cos^2x - 1) (cos^2x + sin^2x)
= 15cos x (cos^2x + sin^2x) / (2cos^2x - 1)
= 15cos x / (2cos^2x - 1)
Therefore, the simplified expression is 15cos x / (2cos^2x - 1).