Factorizing ?

a^2 - ab -5ab + b^2
a (a - b ) -5b (a - b )
(a - b)(a - 5b)

a^2 - 6ab + 5b^2 = (a - b) (a - 5b)

The 2 a terms when multiplied give the a^2 term.

Now we need the factors of 5 (the numbers that when multiplied add up to 5, to give the b^2 term), there is only one option, 1 and 5; luckily these also add up to 6, to give both the middle term (- 6ab) and the last term (+5b^2).

a^2 - 6ab + 5b^2
= a^2 - ab - 5ab + 5b^2
= (a^2 - ab) - (5ab - 5b^2)
= a(a - b) - 5b(a - b)
= (a - b)(a - 5b)

a^2 - 6ab + 5b^2
=(a-5b)(a-b) answer//

a² - 6ab + 5b²

now look at last term is 5 . dont worry about b²
and first term 1
middle term -6
so using first and last term u have to get the middle term
such that the addition is -6 and multiplication is +5

a² +ab - 5ab + 5b²
a(a + b) - 5b ( a + b)
( a - 5b ) ( a + b) answer

a² - 6ab + 5b² = (a-5b)(a-b)