Question

Multiply: 4a + 5b and 4a - 5b

Answer 1

Product of 4a + 5b and 4a - 5b

= 16a² - 25b²

4a + 5b
× 4a - 5b       
16a² + 20ab 
         - 20ab - 25b²
16a²             - 25b²

Answer 2

(4a + 5b) × (4a − 5b)

(x + y) (x − y) = x² − y²

x = 4a and y = 5b

Using the formula: 

(4a + 5b) (4a − 5b) = (4a)² − (5b)²

Simplify each term

(4a)² = 16a²,

(5b)² = 25b²

(4a + 5b) (4a − 5b) = 16a² − 25b²

= 16a² − 25b²