What makes this a perfect square K^2 - 30k +?

225

Step-by-step explanation:

in (a+b)^2, it becomes a^2+2ab+b^2.  A in this case would be "K" and b in this case would be 15.  K^2+2(K)(15)+(15)^2.  That equals k^2+30k+225.  The last part is 225.  

My trick to do this quickly is you get the "2ab" part.  You divide the coefficient by 2 and then square it.  For example, the coefficient in 30K is 30.  30/2 is 15.  15^is 225.

3 is greater then both of those numbers