Question

my question is how to factorise it

Answer 1

here is the answer of your question

Answer 2

16a^4 - 81

(4a^2)^2  - (9)^2

(4a^2 +9) (4a^2-9)

(4a^2+9) {(2a)^2 - 3^2) }         { by using formula a^2-b^2=(a+b)(a-b)}

(4a^2+9) (2a+3) (2a-3)

hope u got it...........:")