Factorise x² + 10x + 16

 
 
This is a quadratic equation.
When we are asked to facorise a quadratic equation, we should label the 3 parts of it a, b and c.
 
x² + 10x + 16
a   b    c         so  a = 1 , b = 10 , c = 16
 
Now, we need to find two numbers that multiply to give c and add up to give b.
Go through the numbers that multiply to give 16 in your head, and add them to see if they give 10...
4 x 4 = 16   but does 4 + 4 = 10 ? No!
16 x 1 = 16 but does 16 +1 = 10?  No!
8 x 2 = 16   but does 8 + 2 = 10 ? Yes!
 
Our factorisation is therefore:
x² + 10x + 16  = ( x + 8 ) ( x + 2 )