5z+15z=840
20z=840 | : 20
z= 42
12,3+1,68=13,98
13,98•2,05=28,659
0,348:2,9=0,12
28,659-0,12=28,539
Ответ:28,539
(sin2a-tg2a)/a^3 = sin2a(cos2a - 1)/(a^3*cos2a) =
sin2a( - 2sin^2a)/(a^3*cos2a) = - 4cosa*sin^3a/(a^3*cos2a)
= ( - 4cosa/cos2a)*(sin^a/a^3)
lim(a->0)(sin2a - tg2a)/a^3 = - 4lim(a->0)(cosa/cos2a)*
lim(a->0)(sina/a)^3 = - 4*1 = - 4