FActorisation

So easy. are you a fool
it is middle term factorization. take (a-3b) as x and (a + 3b) as y.

Hint
7 + 2 = 9

Are you missing a couple of squared symbols? This problem is more fun if (a-3b) is squared in the first term and (a+3b) is squared in the second. The way you have it written, you need to expand all the terms and get:

2a-6b+9a^2-91b^2+7a+21b = 9a^2 + 9a -81b^2 + 15b

And you can't factor that further that I can see.

(a-3b)(a+3b)=a^2-9b^2

2(a-3b)+9(a^2-9b^2)+7(a+3b)

now separate a's and b's

9a^2+9a -81b^2+15b

9a(a+1)-3b(27b-5)

3[3a(a+1)-b(27b-5)]

Rap

2(a-3b)+9(a-3b)(a+3b)+7(a+3b)=2a-6b+9a^2 -81b^2+7a+21b
=9a^2 - 81b^2 + 9a + 15b
=(3a+9b)(3a-9b)+3(3a+5b)
=3((a+3b)(3a-9b)+(3a+5b))
=3((3a+9b)(a-3b)+(3a+5b))
=9((a+3b)(a-3b)+(a+ 5b/3 ))