Math Help - how can I sovle the Sensitivity question

1. 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 $s=1$ equals _____ (units of )/(units of )

Thanks

2. 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 $s=1$ equals _____ (units of )/(units of )

Thanks
Start by using the quotient rule to find dR/ds.

3. 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.....

4. 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.

5. I have tried to submit the negative answer , but it's wrong

6. Originally Posted by shannon1111
I have tried to submit the negative answer , but it's wrong
It would help if from the start you showed all you'd done. What answer have you tried to submit?

7. 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.