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Average leaf width, w (in mm), in tropical Australia1 is a function of the average annual rainfall, r (in mm), so w=f(r). We have f′(1500)=0.0218. (a) What are the units of the 1500? The units of 1500 are mm (of leaf width)/year. mm (of leaf width)/mm (of rain). mm. mm (of rain)/year. mm (of rain)/mm (of leaf width). (b) What are the units of the 0.0218? The units of 0.0218 are mm (of leaf width)/mm (of rain). mm. mm (of leaf width)/year. mm (of rain)/year. mm (of rain)/mm (of leaf width).

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Answer:

a) mm

b) mm (of leaf width)/mm (of rain)

Explanation:


f'(r)=df/dr

This represents the first derivative.

Phisically, represents the rate of variation of the leaf width respect to the rate of variation of the annual rainfall.

The independent variable is r, which units are mm of rain. The year is not needed as the variable is explicitly named "average annual rainfall".

The derivative has units of (mm of leaf)/(mm of rain), as it can be approximated as the division of this two differentials:


[f'(r)]=[df/dr]=([\Delta w])/([\Delta r]) =(mm \,leaf)/(mm\,rain)

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