Answer:
25% decrease
Step-by-step explanation:
Take the original amount of books and subtract the new number of books
20 -15 = 5
Divide by the original amount of books
5/20 = .25
Multiply by 100%
25%
It is a decrease since the amount went down
25% decrease
The function in vertex form is

(refer to your other post I solved it there).
The general form of quadratic equations in vertex form is

, where (h, k) is the vertex of the parabola.
Here, a = 1, h = -6 and k = -54
Therefore, the vertex is (-6, -54) and it is a maximum because a = 1 is postive.
I believe so. (TRUE). a square has all equal sides so if the figure is just alike, its a reg quad.
With mental math, you can perform equations quickly and efficiently. They also help you to develop your own strategies and solve more complex math equations. Hope this helps;)