Explanation:
The rectangle has been divided into a square and three rectangles.
The area of
a square = (x)(x) = x²
a rectangle #1 = (2)(x) = 2x
a rectangle #2 = (3)(x) = 3x
a rectangle #3 = (2)(3) = 6
The area of a large rectangle is the sum of the square area and three rectangles, and is 9 cm². Therefore we have the equation:
x² + 2x + 3x + 6 = 9 subtract 6 from both sides
x² + 5x + 6 - 6 = 9 - 6
x² + 5x = 3