Find the diagonal of the rectangle if one side of the rectangle is 9cm and the other is 3cm larger?

Given:
ABCD- rectangle,
AB = 9 centimeters,
BC = AB + 3 centimeters,
Find the length of the diagonal AC of the rectangle -?
Decision:
1) Consider a rectangle ABCD. Find
BC = AB + 3;
BC = 9 + 3;
BC = 12 centimeters;
2) Consider a right-angled triangle ABC. By the Pythagorean theorem:
AC ^ 2 = AB ^ 2 + BC ^ 2;
AC ^ 2 = 9 ^ 2 + 12 ^ 2;
AC ^ 2 = 81 + 144;
AC ^ 2 = 225;
AC = 15 centimeters.
Answer: AC diagonals = 15 centimeters.