Question 207003
A standard multiplication you should know is {{{(a+b)(a-b) = a^2 - b^2}}} where each of a and b can be any number, variable or other expression (You can FOIL it, but it would be good to learn this formula).
 
In this case, a = x, b = 12, so {{{(x+12)(x-12)=x^2 - 12^2=x^2 - 144}}}.