Math Problem Statement

Ifz=(x+y)e^x,x=2t,y=2−t^2,find dz/dt using the chain rule. Assume the variables are restricted to domains on which the functions are defined.

dz/dt= 

Solution

To find dzdt\frac{dz}{dt} using the chain rule, we need to differentiate z=(x+y)exz = (x + y)e^x with respect to tt, where x=2tx = 2t and y=2t2y = 2 - t^2.

Step-by-step approach:

  1. Identify the expression for zz: z=(x+y)exz = (x + y)e^x

  2. Differentiate zz with respect to tt: By the chain rule, we have: dzdt=zxdxdt+zydydt\frac{dz}{dt} = \frac{\partial z}{\partial x} \cdot \frac{dx}{dt} + \frac{\partial z}{\partial y} \cdot \frac{dy}{dt}

    Now, we need to compute the partial derivatives zx\frac{\partial z}{\partial x} and zy\frac{\partial z}{\partial y}, and also the derivatives dxdt\frac{dx}{dt} and dydt\frac{dy}{dt}.

  3. Find partial derivatives:

    = (x + y)e^x + e^x = (x + y + 1)e^x$$ $$\frac{\partial z}{\partial y} = \frac{\partial}{\partial y} \left( (x + y)e^x \right) = e^x$$
  4. Find the derivatives of xx and yy with respect to tt: dxdt=ddt(2t)=2\frac{dx}{dt} = \frac{d}{dt}(2t) = 2 dydt=ddt(2t2)=2t\frac{dy}{dt} = \frac{d}{dt}(2 - t^2) = -2t

  5. Substitute everything into the chain rule: dzdt=((x+y+1)ex)2+(ex)(2t)\frac{dz}{dt} = \left( (x + y + 1)e^x \right) \cdot 2 + \left( e^x \right) \cdot (-2t)

  6. Substitute the expressions for xx and yy: Since x=2tx = 2t and y=2t2y = 2 - t^2, substitute these into the equation: dzdt=((2t+(2t2)+1)e2t)2+e2t(2t)\frac{dz}{dt} = \left( \left( 2t + (2 - t^2) + 1 \right)e^{2t} \right) \cdot 2 + e^{2t} \cdot (-2t) Simplify the expression inside the parentheses: 2t+2t2+1=t2+2t+32t + 2 - t^2 + 1 = -t^2 + 2t + 3 So, the expression becomes: dzdt=((t2+2t+3)e2t)2+e2t(2t)\frac{dz}{dt} = \left( (-t^2 + 2t + 3)e^{2t} \right) \cdot 2 + e^{2t} \cdot (-2t) Simplify: dzdt=2(t2+2t+3)e2t2te2t\frac{dz}{dt} = 2(-t^2 + 2t + 3)e^{2t} - 2te^{2t} Combine like terms: dzdt=e2t(2(t2+2t+3)2t)\frac{dz}{dt} = e^{2t} \left( 2(-t^2 + 2t + 3) - 2t \right) Simplify further: dzdt=e2t(2t2+4t+62t)\frac{dz}{dt} = e^{2t} \left( -2t^2 + 4t + 6 - 2t \right) dzdt=e2t(2t2+2t+6)\frac{dz}{dt} = e^{2t} \left( -2t^2 + 2t + 6 \right)

Thus, the derivative is: dzdt=e2t(2t2+2t+6)\frac{dz}{dt} = e^{2t} \left( -2t^2 + 2t + 6 \right)

Do you need further details or clarifications on any step?

Here are 5 follow-up questions to explore this topic further:

  1. How does the chain rule work when there are multiple variables involved, like in this case with xx and yy?
  2. How would you compute dzdt\frac{dz}{dt} if we used a different form for xx and yy?
  3. What would happen if the expression for zz included more complex terms like trigonometric functions?
  4. How would you apply the product rule if zz was a product of more complex functions instead of a sum?
  5. Could you simplify this expression for special cases, like when t=0t = 0?

Tip: When working with derivatives, always double-check that you’ve applied the chain rule correctly, especially when dealing with compositions of functions.

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Math Problem Analysis

Mathematical Concepts

Chain Rule
Partial Derivatives
Differentiation with respect to a variable
Exponentials

Formulas

dz/dt = (∂z/∂x)(dx/dt) + (∂z/∂y)(dy/dt)
∂z/∂x = (x + y + 1)e^x
∂z/∂y = e^x

Theorems

Chain Rule
Product Rule

Suitable Grade Level

Grades 11-12