Find the maximum and minimum of 6x-8y

Question

kainui · Answer

So what is 6x-8y? Are you sure you wrote the right thing?

anonymous · Answer

$$f(x)=6x-8y$$
$$f'(x)=6-8dy/dx$$
$$f''(x)=-8 <0$$
You have a maximum at f(x) - actually there must have been a chance of substituting value in x in $$f''(x)$$

anonymous · Answer

The proper steps are,
$$f(x) = \alpha$$
the differentiate the function, then equate it  with zero. So you have a value of x.
Now double differentiate the original function, and substitute the value of x you got in it.
If the resultant value after substitution is  <0 , then its a maximum at x , else its a minimum at x.

kainui · Answer

@Talshiar Those are some pretty nice assumptions you're making. But you know what they say about assumptions...

anonymous · Answer

I think so the question posted here is incomplete, or without any conditions mentioned so i assumed it to be a function of x and differentiated it.

kainui · Answer

Yeah that's why I asked to begin with. I'm not telling you how you shouldn't waste your time though.