Question

Use suitable identities to find the following products :- (3x + 4) (3x – 5)

Answer 1

`(3x + 4) (3x – 5) = 9(x+4/3)(x-5/3)`

By using the identity (x + a)(x + b) = x² + (a + b)x ab,

`9(x+4/3)(x-5/3) = 9[x^2+(4/3-5/3)x+(4/3)(-5/3)]`

                               `= 9[x^2-1/3x-20/9]`

                               `= 9x^2-3x-20`