2. suppose that in the sales tax example, we wanted the output to be the total cost of the piece of merchandise instead of just the tax. let c be the name of the cost function. use the sales tax rate that is in effect where you live. (if you happen to live in a location with no sales tax, use 8%.)
2. if you purchase a cd priced at $13.79, determine the total cost. use functional notation to represent the cost.
3. if you purchase an item costing $59.95, determine the total cost. use functional notation to represent the cost.
4. if the price of an item is p dollars, describe in words how you calculate c(p), the cost of the item.
5. determine a formula for c(p). simplify your formula as much as possible.

let's cover over the formula of the vertex:

y = a(x – h)^2 + k

in this formula, (h,k) are the vertex, always remember that the positive or negative value of the vertex is based on the sign it has.

for example, if the vertex is -3,-6 then both the x and y value would have the positive sign attached to it and if it were a positive x and y value, then a negative sign would be attached to it.

with that being said, for our problem the x value is a positive one so we are looking for a number with a negative sign next to it, in this case the first and second choice.

however, for the first answer choice it isn't quite part of the formula so we know that the answer choice correctly displays the x value.

to confirm, we can see if the -1 fits correctly with the second answer choice, and as mentioned above a negative number will have a positive sign attached to it. so, for our problem we can see that -1 has been changed to +1, so we can confirm that the second answer choice is correct.

hence, our final answer is y=(x - 1)^2 + 1