A melting ice layer A spherical iron ball 8 in. in diameter is coated with a layer of ice of uniform thickness. If the ice melts at the rate of 10 in³/min, how fast is the thickness of the ice decreasing when it is 2 in. thick? How fast is the outer surface area of ice decreasing?
Table of contents
- 0. Functions7h 52m
- Introduction to Functions16m
- Piecewise Functions10m
- Properties of Functions9m
- Common Functions1h 8m
- Transformations5m
- Combining Functions27m
- Exponent rules32m
- Exponential Functions28m
- Logarithmic Functions24m
- Properties of Logarithms34m
- Exponential & Logarithmic Equations35m
- Introduction to Trigonometric Functions38m
- Graphs of Trigonometric Functions44m
- Trigonometric Identities47m
- Inverse Trigonometric Functions48m
- 1. Limits and Continuity2h 2m
- 2. Intro to Derivatives1h 33m
- 3. Techniques of Differentiation3h 18m
- 4. Applications of Derivatives2h 38m
- 5. Graphical Applications of Derivatives6h 2m
- 6. Derivatives of Inverse, Exponential, & Logarithmic Functions2h 37m
- 7. Antiderivatives & Indefinite Integrals1h 26m
- 8. Definite Integrals4h 44m
- 9. Graphical Applications of Integrals2h 27m
- 10. Physics Applications of Integrals 3h 16m
- 11. Integrals of Inverse, Exponential, & Logarithmic Functions2h 34m
- 12. Techniques of Integration7h 39m
- 13. Intro to Differential Equations2h 55m
- 14. Sequences & Series5h 36m
- 15. Power Series2h 19m
- 16. Parametric Equations & Polar Coordinates7h 58m
4. Applications of Derivatives
Related Rates
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Given and , which of the following is the correct value of at ?
A
B
C
D

1
Step 1: Recognize that dy/dx can be computed using the chain rule. Since x = e^t and y = t e^{-t}, we need to find dy/dt and dx/dt first, and then compute dy/dx as (dy/dt) / (dx/dt).
Step 2: Compute dx/dt. Since x = e^t, differentiate x with respect to t to get dx/dt = e^t.
Step 3: Compute dy/dt. Since y = t e^{-t}, apply the product rule: dy/dt = d(t)/dt * e^{-t} + t * d(e^{-t})/dt. This simplifies to dy/dt = 1 * e^{-t} + t * (-e^{-t}) = e^{-t} - t e^{-t}.
Step 4: Substitute dx/dt and dy/dt into the formula for dy/dx: dy/dx = (dy/dt) / (dx/dt). This becomes dy/dx = (e^{-t} - t e^{-t}) / e^t.
Step 5: Simplify the expression for dy/dx. Factor out e^{-t} in the numerator: dy/dx = (e^{-t}(1 - t)) / e^t. Combine the exponents using the property of exponents: dy/dx = e^{-t - t}(1 - t) = e^{-2t}(1 - t). Finally, substitute t = 1 into this expression to evaluate dy/dx at t = 1.
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