Rectangular perimeter 18 cm, has an area of 20 cm 2. Calculate the length of the edge.

Let’s denote the length of the rectangle by the letter a, and the width of the rectangle by the letter b.

The perimeter of the rectangle is 18 cm, let’s make the equation: (a + b) * 2 = 18; a + b = 9.

The area of the rectangle is 20 cm², we make the equation: ab = 20.

The result is a system of equations: a + b = 9; ab = 20.

Let’s solve the system by the substitution method. Let us express b from the first equation and substitute it into the second.

b = 9 – a.

a (9 – a) = 20.

9a – a² – 20 = 0.

a² – 9a + 20 = 0.

D = 81 – 80 = 1 (√D = 1);

a1 = (9 – 1) / 2 = 8/2 = 4.

a2 = (9 + 1) / 2 = 10/2 = 5.

Find the value b: b = 9 – a.

b1 = 9 – a; b = 9 – 4 = 5.

b2 = 9 – 5 = 4.

Answer: the lengths of the sides of the rectangle are 4 cm and 5 cm.