Answer:
225/4
Step-by-step explanation:
When you are trying to find the number to be added to a binomial of the form : [tex]x^2+bx[/tex] in order to make it a perfect square trinomial, all you need to do is to use the square of half of the coefficient b. That is : [tex](\frac{b}{2} )^2[/tex].
In your case this is: [tex](\frac{15}{2} )^2=\frac{15^2}{2^2}=\frac{225}{4}[/tex]
