# how can I sovle the Sensitivity question

• Jun 7th 2009, 06:25 PM
shannon1111
how can I sovle the Sensitivity question
Let R be the reaction of the body to some stimulus of strength s (measured in the appropriate units). The sensitivity S is defined to be the rate of change of the reaction with repect to s. Suppose that, for the particular R and s, the following experimental formula has been used:

R=（90+21s^0.5）/(1+3s^0.5)

The sensitivity S at http://nernst.chem.sfu.ca/cgi-bin/mimetex.cgi?s%3D1 equals _____ (units of )/(units of )

Thanks
• Jun 7th 2009, 06:29 PM
mr fantastic
Quote:

Originally Posted by shannon1111
Let R be the reaction of the body to some stimulus of strength s (measured in the appropriate units). The sensitivity S is defined to be the rate of change of the reaction with repect to s. Suppose that, for the particular R and s, the following experimental formula has been used:

R=（90+21s^0.5）/(1+3s^0.5)

The sensitivity S at http://nernst.chem.sfu.ca/cgi-bin/mimetex.cgi?s%3D1 equals _____ (units of )/(units of )

Thanks

Start by using the quotient rule to find dR/ds.
• Jun 7th 2009, 06:31 PM
shannon1111
Quote:

Originally Posted by mr fantastic
Start by using the quotient rule to find dR/ds.

I know， I got dR/dS = -124.5 /[ (s^ -0.5)(1+3s^0.5)^2]

but when I substitude s=1, I got a negative number.....
• Jun 7th 2009, 06:43 PM
mr fantastic
Quote:

Originally Posted by shannon1111
I know， I got dR/dS = -124.5 /[ (s^ -0.5)(1+3s^0.5)^2]

but when I substitude s=1, I got a negative number.....

I get dR/dS = -124.5 /[ (s^0.5)(1+3s^0.5)^2] (notice, no red negative). So the sensitivity is negative. So what? It's just a number on a scale.
• Jun 7th 2009, 07:03 PM
shannon1111
I have tried to submit the negative answer , but it's wrong(Headbang)
• Jun 7th 2009, 07:09 PM
mr fantastic
Quote:

Originally Posted by shannon1111
I have tried to submit the negative answer , but it's wrong(Headbang)

It would help if from the start you showed all you'd done. What answer have you tried to submit?
• Jun 11th 2009, 06:00 PM
chengbin
I'm getting what mr fantastic got. The answer is a negative stimulus, unless you typed it wrong. It would help if you could type it in Latex.