BC = 13cm

RI = environ 10,7cm

2 = au carré

BC2 = AB2 + AC2

BC2 = 12 au carré + 5au carré

BC = 144 + 25 =169

BC = 169 au carré = 13

RS2 = IS2 + IR2

RI2 = RS2 - IS2

RI2 = 14 au carré - 9 au carré

RI = 196-81 = 115

RI = 115 au carré = 10,7