Need help solving question

Question

The cost C in dollars of operating a certain concrete-cutting machine is related to the number of minutes n the machine is run by the function C(n)=2.2n^2-66n+655. For what number of minutes is the cost of running the machine a minimum? What is the minimum cost?

Answer 1

This question is asking for the minimum value.  If you were to sketch this function, you'd have C (cost) on your y-axis and n (number of minutes) on your x-axis. 

 

The function itself would be concave up (like a smiley face).  Your question is asking for the x-value (number of minutes) and the y-value (cost) at the lowest point of your parabola, the vertex.

 

 

You'll want to use the formula x = -b/2a to find the x-value at the vertex, and then plug that back into the original function to find the y-value. 

 

 

See my answer to your other question for help plugging in those values.