Need Help!!!
A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 2.3 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building? (Round your answer to one decimal place.)

Question

Need Help!!!
A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 2.3 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building? (Round your answer to one decimal place.)

anonymous · Answer

I got -0.8625 and rounded to -0.9. Don't know why it's incorrect

anonymous · Answer

|dw:1350357942997:dw|

anonymous · Answer

$$\frac{2}{x}=\frac{s}{12}$$ and 
is what i get as a start

anonymous · Answer

making 
$$s=\frac{24}{x}$$ you want $s'$ taking derivative we get 
$$s'=-\frac{24}{x^2}x'$$ 
you know $x'=2.3, x=8$ substitution should work

anonymous · Answer

how to you like that, i got the same answer as you

anonymous · Answer

i don't know why it is incorrect either, whatever it is we made the same mistake or, more likely, whatever system you are using wants more or fewer decimals.  who knows?