Quick help please

[robertkoepl]

12B-57. A company produces custom square tiles of side dimension a inches.
The cost per tile is C tile= (a - 6in)^2/(10in^2) + $2. Calculate the tile side dimension a which
minimizes the total cost of t iling a large room.

Cant figure out, coach cant figure out. answer is like 9.33
just realized the bottom is square in. and the top isnt, does that matter

[Shawn]

57) Min/Max so calculus


Find derivative set to zero to minimize it:


A note for understanding: The cost per tile is the function given, but the area covered varies, so in order to properly do the problem you have to divide cost by area to get cost/area (this is what needs to be minimized not cost/tile, which is what you would get if you didn't divide). Feel free to post again if you don't understand my solution or if you have another question.
Edits: Annoying latex.

[BlasianAsian]

Yeah, one more thing. How would you find the derivative of a function with x in the denominator?

[nsguy1350]

Yeah, one more thing. How would you find the derivative of a function with x in the denominator?

If you can't divide through long division, seems like the quotient rule might be useful. Depends on the actual function though.

[Shawn]

Yeah, one more thing. How would you find the derivative of a function with x in the denominator?

Use a calculator or know calculus well. TI-89 can give you algebraic or 84 can use equation solver. An option for solving by hand would be to expand or quotient rule.

[robertkoepl]

What do I do after that cuz I'm still getting 6

[Shawn]

What do I do after that cuz I'm still getting 6

My solution above gets you the correct answer. I don't know what you are doing to get 6? See my solution above, it results in 9.33.

[robertkoepl]

Oh wow. You're definitely right. Thanks!!!