a. BC=rad(12^2+5^2)=rad(144+25)=13
sin B=12/13
cos B=5/13
sin C=5/13
cos C=12/13
tgB=sinB:cosB=12/5
ctgB=5/12
tgC=5/12
ctgC=12/5
b. AC=rad(30^2-18^2)=rad(900-324)=24
sin B=24/30=4/5
cos B=18/30=3/5
sin C=3/5
cos C=4/5
tg B=4/3
ctg B=3/4
tg C=3/4
ctg C=4/3
c. AC=rad( 35^2-28^2)=rad(1225-784)=rad(441)=21
sin B=cos C=21/35=3/5
sin C=cos B=28/35=4/5
tg B=ctg C=3/4
tg C=ctg B=4/3