Answer:
- 8° per hour
Step-by-step explanation:
Given that:
Station A = - 6°
Station B = 2°
Rate of temperature change = x° / hour ; which is the same at both stations
Temperature at station A 3 hours after the recording is the same as the temperature in station B 4 hours after the recording ;
Temperature change in Station A:
-6 + 3x
Temperature change in station B:
2 + 4x
Temperature change in A = temperature change in B
-6 + 3x = 2 + 4x
Collect like terms
3x - 4x = 2 + 6
- x = 8
x = - 8
Hence, the rate of temperature change x in both stations is - 8° per hour


Critical points occur when

, which happens for

and

.
Check the sign of the second derivative at each critical point to determine the function's concavity at that point. If it's concave (

), then a maximum occurs; if it's convex (

), then a minimum occurs.
You have

and so


This means a maximum of

and a minimum of

.