OK. So the cost to manufacture any number 'm' machines is
<span> C(m) = 20m^2 - 830m + 15,000 .
Whatever number of machines you're interested in, you write that number in place of 'm', and this equation tells you the cost for that many.
Examples:
-- The cost to manufacture zero sewing machines ... what the company had to invest in equipment and building space before they could even start manufacturing anything:
</span><span><span>C(m) = 20m^2 - 830m + 15,000
C(0) = 20(0)² - 830(0) + 15,000 = 15,000 .
</span>-- The cost to manufacture one sewing machine ... buy the building, set up the manufacturing equipment, and turn out the first one:
</span><span>C(m) = 20m^2 - 830m + 15,000
C(1) = 20(1)² - 830(1) + 15,000 = 14,190 .
Now, part-a) wants to know the cost to build 75 sewing machines. If you've been paying attention so far, you know you have to take the same equation, and write '75' in place of 'm'.
Now you need to find the number of sewing machines that can be built for the lowest total cost.
</span><span>I'm sure you noticed that the equation for the cost C(m) is a quadratic equation. So if you drew it on a graph, it would be a parabola. It would have a minimum value at some 'm', and for greater 'm', it would start going up again.
(Why should your cost start increasing past some number of sewing machines ? Well, maybe the manufacturing equipment is starting to wear out, and needs repair more often.</span> All of that is actually built into the equation for C(m) . )
Now, I'm not sure what method you've learned for finding the minimum value of a parabola (quadratic equation). Here are the two ways I know:
Way #1). If you've had some pre-calculus, then you'll take the derivative of the equation, set the derivative equal to zero, and that leads you to the minimum:
The equation: <span> C(m) = 20m^2 - 830m + 15,000
Its first derivative: C'(m) = 40m - 830
'C'; is minimum when C'=0 : 40m - 830 = 0
Add 830 to each side: 40m = 830
Divide each side by 40 : m = 20.75
The number of sewing machines manufactured for the minimum total cost is 20 or 21 . </span> Way #2). Really the same as Way-#1 but it's not called 'derivative'.
I looked online for rules of parabolas, and found the one that you may have learned to use:
For the quadratic expression Ax² + Bx + C , the axis (midline) of the parabola is at x = - B / 2A .
That's exactly what we need. Our equation is <span>C(m) = 20m^2 - 830m + 15,000
so the axis of the parabola is at m = - (-830)/2(20)
So basically function of m (f(m) or in this case C(m)) means the price so just input the value you put for m for all the other m's in the problem ex. if you had f(x)=3x and you wanted to find f(4) then you replace and do f(3)=3(4)=12 so f(3)=12 and so on
A. cost of 75 sewing machines 75 is the number you replace m with C(75)=20(75)^2-830(75)+15,000 simplify 20(5625)-62250+15000 112500-47250 65250 the cost for 75 sewing machines is $65,250
B. we notice that in the equation, that the only negative is -830m so we want anumber that will be big enough to make -830m destroy as much of the other posities a possible
-830m+20m^2+15000 try to get a number that when multiplied by 830, is almost the same amount as or slightly smaller than 20m2+15000 so we do this 830m<u><</u>20m^2+15000 subtract 830m from both sides 0<u><</u>20m^2-830m+15000 factor using the quadratic equation which is (-b+ the square root of (b^2-4ac))/(2a) or (-b- the square root of (b^2-4ac))/(2a) in 0=ax^2+bx+c so subsitute 20 for a and -830 for b and 15000 for c you will get a non-real result I give up on this meathod since it gives some non real numbers so just guess
after guessing and subsituting, I found that the optimal number was 21 sewing machines at a cost of 6420
