Question

Expand using the formula:

(4a + 5b − 7) (4a + 5b + 2)

Answer 1

(4a + 5b − 7)(4a + 5b + 2)

= (4a + 5b)(4a + 5b + 2) − 7(4a + 5b + 2)

= [(4a + 5b)(4a) + (4a + 5b) (5b) + (4a + 5b)(2)] − [7(4a) + 7(5b) + 7(2)]

= [16a² + 20ab + 20ab + 25b² + 8a + 10b] − [28a − 35b − 14]

= 16a² + 40ab + 25b² + 8a + 10b − 28a − 35b − 14

= 16a² + 40ab + 25b² + 8a − 28a + 10b − 35b − 14

∴ (4a + 5b − 7) (4a + 5b + 2) = 16a² + 40ab + 25b² − 20a − 25b − 14