Wording of Question tripping me up

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rodneyq

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Please look at the problem:

6. The luminous intensity, I candelas, of a lamp at different voltages V is given by the equation I = 0.0004V2. Find the voltage at which the light is increasing at the rate of 0.2 candelas per volt (i.e., when dI/dV = 0.2).

I know how to differentiate the I= part but don't know where to go from here. Apologies if I've posted this in the wrong place this is my first post on a forum. Cheers in advance for any assistance.
 
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rodneyq said:
Please look at the problem in the attached image. I know how to differentiate the I= part but don't know where to go from here. Apologies if I've posted this in the wrong place this is my first post on a forum. Cheers in advance for any assistance.
Click to expand...
The hint tells you what to do. Since you know how to differentiate, what is dI/dt?
 
dI/dV = 0.0008V. When dI/dV = 0.2 then V = 250 Volts. But how do we get to the 250 easily? Instead of just trying numbers till I get 0.2.
 
rodneyq said:
dI/dV = 0.0008V. When dI/dV = 0.2 then V = 250 Volts. But how do we get to the 250 easily? Instead of just trying numbers till I get 0.2.
Click to expand...

dI/dV = 0.0008 V = 0.2
0.0008 V = 0.2
V = .2/.0008 = 250
 
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