Question

Factorise:-8(a+3b)^2 -18(a-3b)^2

Answer 1

8 (a + 3b)^2 - 18 ( a - 3b)^2

= 8 × [ a^2 + 6ab + 9b^2 ] - 18 × [ a^2 - 6ab + 9b^2

= 8a^2 + 48ab + 72b^2 - 18a^2 + 108ab - 162b^2

= - 10a^2 + 156ab - 90b^2

= -2 ( 5a^2 - 78ab + 45b^2 )

= (-2) ( a - 15b ) ( 5a - 3b)