The perimeter of the rectangle is 30cm. Find its sides if you know that the area of the rectangle is 56 cm2.

To solve the problem, you can draw up a system of equations, since the perimeter of the rectangle is 30 cm and its area is 56 cm², for x and y we take the sides of the rectangle:
2 * (x + y) = 30
x * y = 56;
x = 56 / y
56 / y + y = 15;
56 + y² – 15y = 0;
y1 = 7, y2 = 8.
We take y = 8 cm – the length of the rectangle, then the width is 7 cm.
Answer: 8 cm is the length of the rectangle, 7 cm is its width.