F(x)=-9/x which is equal to:
f(x)=-9x^(-1) So the power rule for differentiation is used...
Power rule: f(x)=x^e, df/dx=ex^(e-1) so:
df/dx=-9(-1)x^(-1-1)
df/dx=9x^(-2) or if you prefer...
df/dx=9/x^2
df/dx(6)=9/36=1/4
7/6 in and 6/7 in is the answer
Answer:
Option 3 - 4 miles
Step-by-step explanation:
Given : In a city, the distance between the library and the police station is 3 miles less than twice the distance between the police station and the fire station. The distance between the library and the police station is 5 miles.
To find : How far apart are the police station and the fire station?
Solution :
Let the distance between police station and fire station be 'x'.
The distance between the library and the police station is 3 miles less than twice the distance between the police station and the fire station.
i.e. 
The distance between the library and the police station is 5 miles.
i.e. 



Therefore, The police and fire stations is 4 miles apart.
So, Option 3 is correct.