Упростите:

а) cosx/1-sinx + cosx/1+sinx

б)

cos^2a - (ctg^2a+1) sin^2a

Вычислите:

5+2tg^2x • cos^2x, если sinx = 0,8

1) cosx / (1 - sinx) + cosx / (1 + sinx) = (cosx (1 + sinx + 1 - sinx)) / (1 - sin^2x) = (2cosx) / (1 - sin^2x) = (2cosx) / (cos^2x) = 2 / (cosx).

2) cos^2 (a) + ctg^2 (a) - 1/sin^2 (a) = cos^2 (a) + ctg^2 (a) - 1-ctg^2 (a) = cos^2 (a) - 1=1-sin^2 (a) - 1=-sin^2 (a)