Объяснение:

1.

в) tgC=AB/AC

2.

5tg45-3cos60=5×1-3×1/2=5-3/2=3,5

3.

<C=90

sinB=0,4

AC=8 cм

АВ=?

sinB=AC/AB

AB=AC/sinB

AB=8 :0,4=20 cм

4.

sina^2+cosa^2=1

cosa^2=1-sina^2

Cosa^2=1-(4/5)^2=1-16/25=9/25

cosa=3/5

tga=sina/cosa=4/5:3/5=4/5×5/3=4/3=1 1/3

ctga=cosa/sina=3/5:4/5=3/5×5/4=3/4