What is a2 - 2ab - 15b2 factored completely?

Answer 1

a^(2)- 2ab - 15b^(2)

When the first term has a coefficient of '1' (a^(2)), then look at the third term.

It is '15'. So we need two numbers that multiply to '15' and 'add/subtract'to '2'.

They are 3. & 5.

So writing up our brackets

( a 5b)(a 3b)

Which signs???

We note from the quadraic , that '15' is negative(-) . So the brackets need one positive(+) and one negative(-)

Since the middle term is also negative(-) , then the larger numerical number takes the negative.

Hence

( a - 5b)(a + 3b)

Done!!!!

Answer 2

a2 - 2ab - 15b2 = (a - 5b)*(a + 3b)