## Diana.xL one year ago http://prntscr.com/8gj6a8 I need a full step explanation.

1. marigirl

|dw:1442308220092:dw| So basically what they are asking is that .. what can you multiple (x+15) by in order to obtain $x^2+18x+45$

2. marigirl

Here our factorising skills can come in handy. Can you factorize (i.e split into a pair of brackets) $x^2+18x+45$ We know from the question one set of these brackets is going to be (x+15)

3. marigirl

Can you see what im getting at? $(x+15)(x+?)=x^2+18x+45$

4. marigirl

I need two numbers that will multiply to 45 and those two very same numbers must add to 18.... I already have a clue to use 15 .. so what will be the other number?

5. Jhannybean

$\text{hi}$

6. anonymous

factorise it

7. anonymous

$x ^{2} + 18x +45$

8. anonymous

do u know how to factorise ?

9. anonymous

so basically you must get two values when add gives you +18 and when multiply you get +45