factorise fully please simple question?

(a – 3)² – 81²
= (a – 3)² – 9²
= (a – 3 – 9)(a – 3 + 9)
= (a – 12)(a + 6)
----

a^2 - b^2 ≡ (a + b)(a - b)

(a - 3)^2 - 81
= [(a - 3) + 9][(a - 3) - 9]
= (a - 3 + 9)(a - 3 - 9)
= (a + 6)(a - 12)

( a – 3 )² – 81

Write 81 in the squared form
= ( a – 3 )² – ( 9 )²

Factorize by the formula a² - b² = ( a + b )( a - b )
= ( a – 3 + 9 )( a – 3 – 9 )
= ( a – 12 )( a + 6 )

Hope this helps
Bye !!

[ ( a - 3 ) - 9 ] [ ( a - 3 ) + 9 ]

[ a - 12 ] [ a + 6 ]

(a -3)^2 -81 = (a-3)^2 -(9)^2
= (a-3 +9)(a-3 -9)
= (a -6)(a -12)
A n s w e r

Pranil is right, but you can also do it the 'basic way' by multiplying it out first...
(a-3)^2-81= a^2-6a+9-81
=a^2-6a-72
=(a-12)(a+6)

a^2-b^2=(a+b)(a-b)
therefore (a-3)^2-(9)^2=[(a-3)+9][a-3-9]
=(a+6)(a-12)