equations..help! #2

[rissagurlie]

The illumination, I, in luxes of a surface d meters from a light source is given by I=kd^-2 where k is a constant based on the intensity of the light source.

A) Solve for k if we know that I=750 luxes at a distance of 2 meters from the light source.

i have:


750=k2^-2

750=k(.25)
/.25 /.25

3000=K is this right?

i dont know how to answer part B of the question

B)If our solar powered calculator needs at least 300 luxes to operate, how far away from the light source can we place the calculator and still be able to operate it?

 

[happy]

Don't double post!


http://www.mathgoodies.com/forums/topic ... C_ID=25951

 

[Denis]

Please rissagurlie, do not post same problem at more than one site.
We thank you in advance for your cooperation.

 

[happy]