How do you decide what is dy/dt, or dx/dt

  • Thread starter AllanW
  • Start date
In summary: This is often what people want to know so they can predict y for a given value of t. This is why it is the first thing you are taught when you study rates of change for real-world models.
  • #1
AllanW
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Homework Statement


if y=2t+3 and x=t^2, find dy/dx

Homework Equations


dy=dy/dt*dt/dx

The Attempt at a Solution


dy/dt=2
dx/dt=2t
therefore dy/dx=1/t
what I don't understand is how the dy/dt etc. is found when attempting this problem[/B]
 
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  • #2
AllanW said:

Homework Statement


if y=2t+3 and x=t^2, find dy/dx

Homework Equations


dy=dy/dt*dt/dx

The Attempt at a Solution


dy/dt=2
dx/dt=2t
therefore dy/dx=1/t
what I don't understand is how the dy/dt etc. is found when attempting this problem[/B]
Well, look at each equation in turn

The first equation is y = 2t + 3. What is dy/dt?

If this equation were written y = 2x + 3, would you have any problem finding dy/dx?

The second equation is x = t2

What if you wanted to find dy/dx for y = x2 ?

The rules of differentiation that you are supposed to learn are written around finding the change in the dependent variable with respect to the change in the independent variable. Since y is usually the dependent variable and x is the independent variable, the rules all state dy/dx = whatever.

For example, if y = xn, then dy/dx = n ⋅ xn-1
 
  • #3
AllanW said:
what I don't understand is how the dy/dt etc. is found when attempting this problem
Do you know how to differentiate the formula 2t+3 with respect to t?
 
  • #4
i understand differentiation in that you could find the derivative by going (2*1)t^(1-1) =2 I'm not clear on how it relates to dy/dt and combining it with dx/dt
 
  • #5
i suppose what I am asking would be; what does dy/dt mean? I can't wrap my head around the explanation in my textbook and I am looking for a dumbed down version
 
  • #6
AllanW said:
i suppose what I am asking would be; what does dy/dt mean
It is the rate of increase of y as t increases. Loosely put, it is the size of the tiny increase in y that would arise from making a tiny increase to t and putting that in the formula for y. If you do a line graph of y on the vertical axis against t on the horizontal axis it is the slope (gradient) of the line.
 

1. What is dy/dt and dx/dt?

dy/dt and dx/dt are both mathematical notations used to represent the rate of change of a dependent variable y and an independent variable x, respectively, with respect to time t. They are commonly used in calculus and physics to calculate the instantaneous rate of change of a variable at a specific point in time.

2. How do you calculate dy/dt and dx/dt?

To calculate dy/dt and dx/dt, you need to take the derivative of the function with respect to time t. This can be done using the rules of calculus, such as the power rule or the chain rule. Once you have the derivative, you can substitute the given value of t to find the instantaneous rate of change at that specific point in time.

3. When is it necessary to use dy/dt and dx/dt?

Dy/dt and dx/dt are commonly used in situations where the rate of change of a variable is continuously changing, such as in motion or growth problems. They are also used in differential equations to describe the relationship between variables and their rates of change.

4. What is the difference between dy/dt and dx/dt?

The main difference between dy/dt and dx/dt is the variable they represent the rate of change for. Dy/dt represents the rate of change of a dependent variable y, while dx/dt represents the rate of change of an independent variable x. However, both notations are used to calculate the instantaneous rate of change at a specific point in time.

5. Can dy/dt and dx/dt have negative values?

Yes, dy/dt and dx/dt can have negative values. This indicates that the variable is decreasing at the given point in time. Positive values indicate an increasing variable, while a value of zero indicates no change. It is important to pay attention to the sign of dy/dt and dx/dt when interpreting the rate of change in a problem.

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