What is the expression in factored form?
x^2 + 13x + 42

Question

What is the expression in factored form? 
x^2 + 13x + 42

anonymous · Answer

(x+6)(x+7)

anonymous · Answer

How did you get that, @henryrodriguez713 ? ( http://openstudy.com/code-of-conduct )

appleduardo · Answer

6+7 = 13, 6*7 = 42 :P so henry is right, thats the factored form

anonymous · Answer

Sorry! Went to shower. Umm... This should help you with remembering the process of factoring quadratics. AND just know that if there is no "a" it's understood to represent 1 and if it's 1 you don't really have to divide, since 6/1 is 6. 
$$f(x)=ax^2 + bx +c$$
MFDARM:
My            M:ultiply by a*c
Father       F:ind the factors of ac that add to b 
Drives       D:ivide by a
A               This a  <---
Red          R:educe fractions 
Mustang   M:ake into factors: put x on bottom and read up. 

$$f(x)=ax^2 + bx +c$$
$$f(x)=x^2 + 13x + 42$$
 
a=1      b=13   c=42       (Note: there is always an invisible 1 at "a")

M: 1*42=42
F: 42                   ** (NOTE: While getting the factors, add them and see if they add to 13)**
  1 * 42      (1+42=43) NOT A FACTOR; doesn't add to 13 
  2 * 21      (2+42= 44) NOT A FACTOR; doesn't add to 13
  3 * 14       (3+14=17) NOT A FACTOR; doesn't add to 13.( @thispointyouknowyou're close
  6 * 7          (6+7=14) DING! DING! DING! 

 Now divide by "a"  $$\frac{ 6}{ 1x}  \frac{ 7 }{ 1x }$$   = (x+6)(x+7)


So, (x+6)(x+7) and if you work it out you see it adds back to the original equation. 
                                                          
NOTE: I know it doesn't make sense to divide by a, but it will help when a is 5 or 6 or 9 and so on.