1) AΔ ABC / AΔ A'B'C'= k²
AΔ ABC / AΔ A'B'C' = 25/16
k²= 25/16 ⇒k= 5/4
k=AB/ A'B'= AC/A'C'= BC/B'C'
AB/A'B'= AC/A'C'= BC/B'C'=5/4
2)ΔABC
a,b,c-laturile triunghiului
a,b,c,dp cu 5,12,13
a/5=b/12=c/13=k
a=5k <=> a²= 25k²
b=12k <=> b²= 144k²
c=13k <=> c²= 169k²
a²+b²=c²
25k²+144k²=169k² ⇒ΔABC-dreptunghic, mas<A=90 grade