OG11-紫91 (已搜索過，不明白題目意思)

Kath1985

OG11-紫91
For a light that has an intensity  of 60 candles at tis source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant.  If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
A 3/10 candle
B 1/2 candle
C 1 candle
D 2 candle
E 3 candle
答案為A

想請牛牛們幫我解釋題目意思 感激~

kingapple25

有一光源，亮度为60，距光源d处的亮度为S=60k/d^2, k是常数，如果在距这个光源2 feet处的亮度是30，那么距此光源20 feet处的亮度是多少？

Kath1985

擱了三天 多謝kingapple的解釋  這會檢討才看懂