Tg B =3/4
Tg B =AC/AB
3/4= AC/12=>AC = 3×12/4= 9 cm
In ∆ABC dr =>TP
AB² +AC² =BC²
12²+9²=BC²
BC²= 144+81
BC² =225
BC=√225
BC=15 cm
P ABC =AB +AC+BC =12+9+15=36 cm
sin B = AC/BC
sin B = 9/15
sin B=3/5
cos B =AB/BC
cos B =12/15
cos B=4/5
ctg B = AB/AC
ctg B= 12/9
ctg B=4/3