Question

The daily production cost, C, for x units is modeled by the equation: C = 200 – 7x + 0.345x2 Explain how to find the domain and range of C

Answer 1

domain is the sex of x values that are feasible. this is all of the positive integer values + 0, in case you only consider that can produce whole units.

range is the set of possible results for c(x), possible costs.

you can derive this from the fact that c(x) is a parabole and you can draw it, for which you can find the vertex of the parabola, the roots, the y intercept, the shape. also limit the costs to be positive.

you can substitute some values for x to help you, for example.

x y
0 200
1 200 - 7 + 0.345 = 193.345
2 200 - 14 + .345(4) = 187.38
3 200 - 21 + .345(9) = 182.105

the function does not have real roots, then the costs never decrease to 0.

the function starts at c(x) = 200, decreases until the vertex, (x = 10, c = 164.5) and starts to increase

then the range goes to 164.5 to infinity, limited to the solution for x = positive integers.

Answer 2

This is a quadratic function, which is usually defined on all reals. But, the domain is restricted to x>=0 because it does not make sense to produce a negative number of units.

Find the vertex of the parabola at

(10.14, 164.5)

Since the parabola opens up, the range is y>=164.5

Explanation: