Question

using identities (3a+5)(3a-5)​

Answer 1

Answer:

9a² - 25

Step-by-step explanation:

(3a + 5) (3a - 5)

There are 2 methods for this one:

1. The easier one

Memorise this formula first

a² - b² = (a + b) (a -b)

So in our question

a = 3a and b = 5

so the answer is

(3a)² - 5²

= 9a² - 25

2. The difficult one

This one takes a lot more time

(3a + 5) (3a - 5)

= 3a (3a - 5) + 5 (3a - 5)

= 3a × 3a - 3a × 5 + 5 × 3a - 5 × 5

= 9a² - 15a + 15a - 25

= 9a² - 25

I personally prefer the first one but

Have a good day :)