Question

y2 - 7y - 18 factorise​

Answer 1

Answer:

y^2 - 9y + 2y - 18

= y (y - 9) + 2 (y - 9)

= (y + 2) (y - 9)

Answer 2

Answer:

y² - 7y - 18 = (y - 9)(y + 2)  

Step-by-step explanation:

We are given following mathematical expression for factorization

y² - 7y - 18

Since

y²×-18 = -18y²

So we have to write -7y into two parts in such a way that

product of them is equal to -18y² and addition of them is equal to -7y

Thus

We make following parts

-7y = - 9y + 2y

See

-9y×2y = -18y²

Hence

The expression becomes

y² - 7y - 18 = y² - 9y + 2y - 18

                  = y(y - 9) + 2(y - 9)

                  = (y - 9)(y + 2)

So

y² - 7y - 18 = (y - 9)(y + 2)  

Thus factorization of y² - 7y - 18 is equal to (y - 9)(y + 2)