# Differentiation rule ?

1. Oct 7, 2004

### cowgiljl

f(t) = 400t+70/t+1 represents the temp. in an oven and f(t) is in F degrees

first i used the quotient rule and got 330/(t+1)^2 = f'(t)

A) the rate of change in temp of the ove with respect to the time of 2 minutes after turnig the oven on and at 10 minutes

i pluged 2 and 10 in for t in the equation above

330/(2+1)^2 = = 36.67 F degrees per min

330/(10+1)^2 == 2.73 F degrees per min

B) fined the rate of change of temp when the oven is 350 degrees

i plugged in 350 where f(t) is

and got t = 5 min

thanks joe

2. Oct 7, 2004

### NateTG

Hmm. That's odd. I get a different answer for $$f'(t)$$. You might want to check your work. (Even if I use $$f(t)=400t + \frac{70}{t+1}$$ rather than $$f(t)=400t + \frac{70}{t} + 1$$.)

For part B:
$$f(5)=400 \times 5 + \frac{70}{5} + 1=2000+12+1=2013$$
So, clearly t=5 is not the correct time.

3. Oct 7, 2004

### ReyChiquito

I guess he was saying f(t)=(400t+70)/(t+1)