Calculus 1 : How to write equations

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #195 : Writing Equations

My friend has  dollars at time  days. She earns  dollars every day, and spends  dollars every day (so at day , she has  dollars). Write an equation for how much money she has at time .

Possible Answers:

Correct answer:

Explanation:

My friend starts off with  dollars, and every day, she makes a net  dollar. This is because she earns three dollars and spends one dollar.

So, we need an equation that reflects that she has *(number of days), which is given by

.

Example Question #191 : Writing Equations

Identify the inner and the outer functions of the following equation (let  be the outer equation and  be the inner equation:

Possible Answers:

Correct answer:

Explanation:

The first section of the equation to be resolved (in this case 1-4x) is the innermost function and the second section to solve is the outer function. So:

becuase g(x) must be performed first before plugging it into f(x).

Example Question #201 : Writing Equations

Identify the inner and the outer functions of the following equation (let  be the outer equation and  be the inner equation:

Possible Answers:

Cannot be determined.

Correct answer:

Explanation:

The first section of the equation to be resolved (in this case 2x^3+5) is the innermost function and the second section to solve is the outer function.

So:

becuase g(x) must be performed first before plugging it into f(x).

Example Question #202 : Writing Equations

Identify the inner and the outer functions of the following equation (let  be the outer equation and  be the inner equation:

Possible Answers:

Cannot be determined.

Correct answer:

Explanation:

The first section of the equation to be resolved (in this case pi * x) is the innermost function and the second section to solve is the outer function.

So:

becuase g(x) must be performed first before plugging it into f(x).

Example Question #203 : Writing Equations

Derive the equation for the function of the .

Possible Answers:

None of these

Correct answer:

Explanation:

By the quotient rule, the derivative of

 

The derivative of sin is cos and the derivative of cos is -sin. Thus the derivative of cot(x) is

By the trigonometric identities this is equal to .

Example Question #11 : How To Write Equations

Suppose Charlie deposits  per month into an account that contains a starting balance of 

Which of the following is a correct initial condition that when coupled with the differential equation from the previous question, will yield a specific solution to the scenario described above?

Possible Answers:

Correct answer:

Explanation:

Here we are looking for an initial condition that describes the balance of the account at a specific time. We are given the information that the account starts with  initially. So at time  years, we know that the amount of money in the account is . Therefore, we can write 

Example Question #204 : Writing Equations

Suppose Charlie deposits  per month into an account that contains a starting balance of 

Which of the following is a differential equation that best models the amount of money, , in the account after  years? 

Possible Answers:

Correct answer:

Explanation:

Here we are writing a differential equation in the units of dollars per year. This means that we need to reconcile our units to get the amount deposited each year. ,

so the yearly rate of change of money in the account,

.

The starting balance is our initial condition and does not tell us about the change in money in the account, so is not included in our differential equation.

Example Question #2285 : Calculus

Find the implicit derivative  of  at the point .

Possible Answers:

Correct answer:

Explanation:

Use implicit differentiation to find  of  which means to take the derivative of each term in the function with its respective part.

It is simpfied to 

.

It is then further simplified to 

,

then to

 ,

then to

.

Plugging in  into the equation gives the value of  .

Example Question #2286 : Calculus

If  and , then what is ?

Possible Answers:

Correct answer:

Explanation:

First we need to find , which is .

Then we find , which equals to 

.

We used the power rule and the product rule to find the derivatives.

Power Rule: 

Product Rule: 

Example Question #2287 : Calculus

, find .

Possible Answers:

Correct answer:

Explanation:

Our starting function is  in order to create an easier function we will want to take the natural log of both sides. Taking the natural log will bring the exponet infront creating a product for which we can more easily differentiate.

Next take the natural log of both sides which results in the following,

 .

Now differentiate both sides with respect to x. 

, and when one isolates .

After isolating  make sure to replace the y term in terms of x.

 

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