Factorise 64-81q^ please help as I am totally stuck on this maths question?

a^2 - b^2
= (a + b)(a - b)
= a^2 - ab + ab - b^2
= a^2 - b^2
This calculation is known as the Difference of Two Squares or Difference of Perfect Squares (DOTS or DOPS).

64 - 81q^2
= (8)^2 - (9q)^2
= (8 + 9q)(8 - 9q)

If you still don't understand it, feel free to email me with any questions.

This is a difference of 2 squares.
64 - 81q^2

(8 - 9q) (8 + 9q)

Assuming that you mean :-
64 - 81 q ²
( 8 - 9 q ) ( 8 + 9 q )

a^2 - b^2 = (a + b)(a - b)

64 - 81q^2
= 8^2 - (9q)^2
= (8 + 9q)(8 - 9q)