a^2+b^2=11^2=121a^2+c^2=19^2=361b^2+c^2=20^2=400d^2=a^2+b^2+c^2=1/2((a^2+b^2)+(a^2+c^2)+(b^2+c^2))
d=1/2(a^2+b^2+c^2)=1/2(11^2+19^2+20^2)=1/2(121+361+400)=1/2*882=441
d=21
a^2+b^2=11^2=121
a^2+c^2=19^2=361
b^2+c^2=20^2=400
d^2=a^2+b^2+c^2=1/2((a^2+b^2)+(a^2+c^2)+(b^2+c^2))
d=1/2(a^2+b^2+c^2)=1/2(11^2+19^2+20^2)=1/2(121+361+400)=1/2*882=441
d=21