help me figure out the partial derivative wrt x of y/(100-x)

[simon16]

Hi, look at the attachment please. The original question is the partial derivative wrt x of y/(100-x). I follow until the end until it seems like the negative signs don't cancel out...Shouldn't the answer be y/(100-x)^2 ? not y/(x-100)^2.

thanks in advance!

 

[Deleted member 4993]

Hi, look at the attachment please. The original question is the partial derivative wrt x of y/(100-x). I follow until the end until it seems like the negative signs don't cancel out...Shouldn't the answer be y/(100-x)^2 ? not y/(x-100)^2.

thanks in advance!

The rule to follow is:

(a - b)² = (b - a)²

Prove it to yourself by expanding both sides.

 

[Steven G]

Hi, look at the attachment please. The original question is the partial derivative wrt x of y/(100-x). I follow until the end until it seems like the negative signs don't cancel out...S(a - b)²the answer be y/(100-x)^2 ? not y/(x-100)^2.

thanks in advance!

You are in Calculus and have not realized that (a - b)² = (b - a)²

You should know that (xy)² = x² * y²

Now (a-b) = (-1)*(b-a) so (a - b)² = (-1)²(b - a)²= 1*(b - a)²= (b-a)²

So there is the proof that it is true!

 

[simon16]

Hi, look at the attachment please. The original question is the partial derivative wrt x of y/(100-x). I follow until the end until it seems like the negative signs don't cancel out...Shouldn't the answer be y/(100-x)^2 ? not y/(x-100)^2.

Thanks man, jumped out at me when I got back to my book, guess I was at the end of a long day haha.

 

[simon16]

You are in Calculus and have not realized that (a - b)² = (b - a)²

You should know that (xy)² = x² * y²

Now (a-b) = (-1)*(b-a) so (a - b)² = (-1)²(b - a)²= 1*(b - a)²= (b-a)²

So there is the proof that it is true!

Thanks for telling me what I should know and being a [deleted] for no reason always appreciated

 

[stapel]

Thanks for telling me what I should know and being a [deleted] for no reason always appreciated

It is to be regretted that you take offense at being advised that one needs a firm grasp of algebra before being able to succeed in calculus. But this is the truth. Please do be sure to review your algebra, as this will be crucial in your success (or failure) going forward.

Have fun!