16.9. cos 2a = (1-tg^2 a)/(1+tg^2 a) = (1-0,04)/(1+0,04) = 0,96/1,04 = 12/13
2/(3 + 4cos 2a) = 2/(3 + 4*12/13) = (2*13)/(3*13 + 4*12) = 26/87
16.10. (sin(a/2) + cos(a/2))^2 = 1,4^2
sin^2(a/2) +2sin(a/2)*cos(a/2) + cos^2(a/2) = 1 + sin a = 1,4^2 = 1,96
sin a = 1,96 - 1 = 0,96