Cost is in dollars and x is the number of units. Find the marginal cost functions MC for the given cost function. C = 700 + 22x + 6x^3 MC =
first I tried 22+12x^2 but i just realized you bring down the exponential power down and subtract it by one then which. igot 22+9x^2 but its wrong
how come 22+9x^2 is wrong
Let´s say you have a polynomial function $f_n(x)=a_n\cdot x^n + a_{n-1}\cdot x^{n-1} + \dotsb + a_2 x^2 + a_1 \cdot x + a_0$, then the derivative w.r.t. $x$ is
$$f_n'(x)=a_n \cdot n\cdot x^{n-1} + a_{n-1}\cdot(n-1)\cdot x^{n-1} + \dotsb + a_2\cdot 2\cdot x^{2-1} + a_1 $$
$$f_n'(x)=a_n \cdot n\cdot x^{n-1} + a_{n-1}\cdot(n-1)\cdot x^{n-1} + \dotsb + a_2\cdot 2\cdot x + a_1 $$
In your case it is $n=3, a_3=6, a_2=0, a_1=22$ and $a_0=700$
$$f_3(x)=C(x)= a_3 \cdot x^3+a_2 \cdot x^2 + a_1 \cdot x + a_0=6 \cdot x^3 + 22\cdot x + 700$$
And therefore the derivative w.r.t $x$ is
$$f_3'(x)=C'(x)= a_{3}\cdot 3\cdot x^{2} + a_2\cdot 2\cdot x + a_1=6 \cdot 3\cdot x^2 + 22=18 \cdot x^2 + 22$$
I guess that you had a miscalculation at $6\cdot 3=18\neq 9$
