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Monica [59]
3 years ago
15

A cold drink is poured out at 52°F. After 2 minutes of sitting in a 72°F room, its temperature has risen to 55°F. Find an equati

on for the drink's temperature at any time t. (t) =
Mathematics
1 answer:
I am Lyosha [343]3 years ago
7 0

Answer:

The model for the temperature of the drink can be written as

T=72-20e^{-0.08t}

Step-by-step explanation:

For a cold drink in a hotter room, we can say that the rate of change of temperature of the drink is proportional to the difference of temperature between the drink and the room.

We can model that in this way

\frac{dT}{dt}=k*(T_r-T)

If we rearrange and integrate

\int\frac{dT}{(T-Tr)} =-k*\int dt\\\\ln(T-T_r)=-kt+C1\\\\T-T_r=Ce^{-kt}\\\\T=T_r+Ce^{-kt}

We know that at time 0, the temperature of the drink was 52°F. Then we have:

T=T_r+Ce^{-kt}\\\\52=72+Ce^0=72+C\\\\C=-20

We also know that at t=2, T=55°F

T=T_r+Ce^{-kt}\\\\55=72-20e^{-k*2}\\\\e^{-k*2}=(72-55)/20=0.85\\\\-2k=ln(0.85)=-0.1625\\\\k=0.08

The model for the temperature of the drink can be written as

T=72-20e^{-0.08t}

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mars1129 [50]

Answer:

Step-by-step explanation:

Given:

x = 2cost,

t = (1/2)arccosx

y = 2sint

dy/dx = dy/dt . dt/dx

dy/dt = 2cost

dt/dx = -1/√(1 - x²)

dy/dx = -2cost/√(1 - x²)

Differentiate again to obtain d²y/dx²

d²y/dx² = 2sint/√(1 - x²) - 2xcost/(1 - x²)^(-3/2)

At t = π/4, we have

(√2)/√(1 - x²) - (√2)x(1 - x²)^(3/2)

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2 years ago
Some kids are selling lemonade for $1.50 per cup at a high
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A function that would represent profit based on the number of cups of lemonade is Profit = 1.5n - 14

<u>Solution:</u>

Given, Some kids are selling lemonade for $1.50 per cup at a high school baseball game.  

They spent $14 on all of the items needed for the lemonade stand (cups, lemonade, table oth, sign, etc)

We have to create a function that would represent profit based on the number of cups of lemonade

Now, let the number of cups sold be "n"

Then , we know that,<em> profit = selling price – cost price  </em>

Profit = number of cups sold x price per cup – cost price

Profit = n x $ 1.5 – $ 14  

Profit = 1.5n – 14

Hence, the function is Profit = 1.5n - 14

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2 years ago
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Is the graph of y = sin(x^4) increasing or decreasing when x = 10? Is it concave up or concave down?
Tanzania [10]
y=\sin(x^4)
\implies y'=4x^3\cos(x^4)
\implies y'=12x^2\cos(x^4)-16x^6\sin(x^4)

At x=10, you have

y'(10)=4000\cos(10^4)

The trick to finding out the sign of this is to figure out between which multiples of \dfrac\pi2 the value of 10^4 lies.

We know that \cos x>0 whenever -\dfrac\pi2+2n\pi, and that \cos x whenever \dfrac\pi2+2n\pi, where n\in\mathbb Z.

We have

10^4=\dfrac{k\pi}2\implies k=\dfrac{2\times10^4}\pi\approx6366.2

which is to say that \dfrac{6366\pi}2, an interval that is equivalent modulo 2\pi to the interval \left(\pi,\dfrac{3\pi}2\right).

So what we know is that 10^4 corresponds to the measure of an angle that lies in the third quadrant, where both cosine and sine are negative.

This means y'(10), so y is decreasing when x=10.

Now, the second derivative has the value

y'=12\times10^2\cos(10^4)-16\times10^6\sin(10^4)

Both \cos(10^4) and \sin(10^4) are negative, so we're essentially computing the sum of a negative number and a positive number. Given that \sin x>\cos x for \pi, and \cos x>\sin x for \dfrac{5\pi}4, we can use a similar argument to establish in which half of the third quadrant the angle 10^4 lies. You'll find that the sine term is much larger, so that the second derivative is positive, which means y is concave up when x=10.
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