The sides of the rectangle are 16 and 12. What is the diagonal and S of the rectangle.

From the condition it is known that the sides of the rectangle are 16 and 12. In order to find the diagonal of the rectangle, consider a right-angled triangle formed by the sides of the rectangle and the diagonal.
The sides of the rectangle are the legs of the right triangle, and the diagonal of the rectangle is the hypotenuse.
To find the hypotenuse, we will use the Pythagorean theorem.
The sum of the squares of the legs is equal to the square of the hypotenuse.
a ^ 2 + b ^ 2 = c ^ 2;
16 ^ 2 + 12 ^ 2 = c ^ 2;
256 + 144 = c ^ 2;
c ^ 2 = 400;
c = 20 diagonal of the rectangle.
We look for the area by the formula:
S = a * b = 16 * 12 = 192 sq. units