r =aria / semiperimetrul
1 aria = a²√3 /4 si semiperim = 3a /2 ⇒ r = ( a²√3 /4 ) : ( 3a /2)
r= a√3 /6
2. semip= ( 12+10+10 ) :2 = 32 :2 =16
aria= √16·√4·√6·√6 =4·2·6=48 r = 48 : 16 =3
3 aria = bc /2 r = [ bc /2 ] : ( a+b+c )/2
r =bc / ( a+b+c )
4. semip=( 4+5+7 ) :2 =8
aria =√8·√4·√3·√1=4√6 r = 4√6 : 8 = √6/2