SOLUTION: Hello, I've tried working this problem out, but my answers are coming out strange and I'm getting really confused. If anyone can help, I'll appreciate it so much! Problem: The

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Hello, I've tried working this problem out, but my answers are coming out strange and I'm getting really confused. If anyone can help, I'll appreciate it so much! Problem: The       Log On


   

Question 1056462: Hello, I've tried working this problem out, but my answers are coming out strange and I'm getting really confused. If anyone can help, I'll appreciate it so much!
Problem: The illumination provided by a car's headlight varies inversely as the square of the distance from the headlight. A headlight produces 15 foot-candles (fc) at a distance of 20ft. What will the illumination be at 50 ft?
Again, thank you so much and I really appreciate any help! Thank you
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
[ illumination ] = k
+15+=+k%2A%28+1%2F+20%5E2+%29+
( note that +k+ is the constant of proportionality )
+15+=+k%2A%28+1%2F400+%29+
+k+=+6000+
--------------------------
given:
+d+=+50+ ft
-----------------
Let +x+ = illumination in foot-candles
+x+=+k%2A%28+1%2F50%5E2+%29+
+x+=+k%2A%28+1%2F2500+%29+
+x+=+6000%2A%28+1%2F2500+%29+
+x+=+2.4+
2.4 footcandles at 50 ft
---------------------------
I can plot illumination on the vertical axis and
distance on the horizontal axis:
+graph%28+600%2C+400%2C+-7%2C+70%2C+-3%2C+30%2C+6000%2A%28+1%2Fx%5E2+%29+%29+