[tex]d= \sqrt{l^{2}+L^{2}+h^{2}}
[/tex]
dar din enunt d=13 cm
[tex][ \sqrt{l^{2}+L^{2}+h^{2}}] ^{2} =13^{2} \\ \\
l^{2}+L^{2}+h^{2}}=169
[/tex]
dar din enunt (l+L+h) = 19 cm
[tex](l+L+h) ^{2} =19 ^{2} \\ \\ (l+L+h) ^{2} =361
[/tex]
utilizam formula:(a+b+c)²=(a+b+c)(a+b+c)=a²+ab+ac+ab +b²+bc+ac
+bc+c²=a²+b²+c²+2ab+2bc+2ac
=a²+b²+c²+2(ab+bc+ac)
deci
(a+b+c)²=a²+b²+c²+2(ab+bc+ac)
[tex](l+L+h) ^{2} =361[/tex] devine:
(L²+l²+h²)+2(L·l+L·h+l·h)=361
169+Atot=361
Atot=361-169
Atot=192 cm²
