Given : ABCD is a rhombus and perimeter(ABCD) = 26 cm and BD = 5 cm To find : AC = ? Solution : Diagonals of a rhombus bisect each other at right angle. => BE = $$frac{5}{2}=2.5$$ cm and side of rhombus = AB = $$frac{26}{4}=6.5$$ cm Thus, in right $$ riangle$$ AEB, => $$(AE)^2=(AB)^2-(BE)^2$$ => $$(AE)^2=(6.5)^2-(2.5)^2$$ => $$(AE)^2=42.25-6.25=36$$ => $$AE=sqrt{36}=6$$ cm $$ herefore$$ AC = $$2 imes6=12$$ cm => Ans - (B)