Question

Use the formula to multiply:

(9) (11 + y) (y – 9)

Answer 1

As (x + a) (x + b) = x² + (a + b)x + ab

So, (11 + y) (y – 9) = (y + 11) (y – 9)
= y² + [11 + (–9)]y – 99
= y² + 2y – 99

∴ (11 + y) (y – 9) = y² + 2y – 99