Question

In the function f(x) = 4(x^2 − 6x +___ ) + 20, what number belongs in the blank to complete the square?

Answer 1

hint:
\[x^2+kx+(\frac{k}{2})^2=(x+\frac{k}{2})^2\]
you have
\[x^2-6x+...\]
compare this to the left hand side of the equation I wrote

Answer 2

and whatever you add in you subtract out