SOLUTION: Hello again I need to complete this task: the illuminance E at a point on a surface is given by the formula E=I/d^2 Where E=Illuminance in Lux I= luminointensity of the light c

Algebra ->  Square-cubic-other-roots -> SOLUTION: Hello again I need to complete this task: the illuminance E at a point on a surface is given by the formula E=I/d^2 Where E=Illuminance in Lux I= luminointensity of the light c      Log On


   

Question 936684: Hello again I need to complete this task:
the illuminance E at a point on a surface is given by the formula E=I/d^2
Where E=Illuminance in Lux
I= luminointensity of the light cource in candelas
d=distance in meters
Rearrange this formula to make d the subjet and find the value of d given that E=25 Lux and I=100 candelas.
This is my way how i do it:
E=I/d^2
25=100/d^2
d^2=100/25
d^2-4
2^2=4
and my tutor write to me "Incorrect, you have not follow the full process"
Please correct my work I not sure what i do wrong.
Thank You
Found 2 solutions by Fombitz, rothauserc:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
The tutor may have wanted you to re-arrange the formula first and then solve(?).
E=I%2Fd%5E2
d%5E2=I%2FE
highlight%28d=sqrt%28I%2FE%29%29
.
.
.
d=sqrt%28100%2F25%29
d=sqrt%284%29
highlight%28d=2%29m

Answer by rothauserc(4718) About Me  (Show Source):
You can put this solution on YOUR website!
E = I/d^2
we need to solve for d
multiply both sides of = by d^2
(d^2)*E = I
d^2 = I/E
d = square root(I/E), we are given E=25 Lux and I=100 candles, therefore
d = square root(100/25) = 10/5 = 2 meters