For f(x, y) = 2xy − 4x³ − 5y³, find the partial derivative ∂f/∂y at the point (−1, 2).
Multivariable calculus worksheet with answers
1.Easy
f(x, y) = 2xy − 4x³ − 5y³P = (−1, 2)
fy(−1, 2) =
2.Easy
For f(x, y) = −x²y³ − 5x² − 4y² + 4xy, find the partial derivative ∂f/∂x at the point (−1, 1).
f(x, y) = −x²y³ − 5x² − 4y² + 4xyP = (−1, 1)
fx(−1, 1) =
3.Medium
For f(x, y) = 2 ln(x² + 3y²), find the directional derivative Duf at P(−1, 1) in the direction towards Q(−4, 4).
f(x, y) = 2 ln(x² + 3y²)P = (−1, 1)Q = (−4, 4)
Duf =
4.Medium
For f(x, y) = −y·exy, find the directional derivative Duf at P(0.5, 0.5) in the direction towards Q(−3.5, −0.5).
f(x, y) = −y·exyP = (0.5, 0.5)Q = (−3.5, −0.5)
Duf =
5.Hard
The marked points are the critical points of f(x, y) = x³ + y³ + 3xy. Click the saddle point.
f(x, y) = x³ + y³ + 3xy
- 1A (0, 0)
- 2B (−1, −1)
6.Hard
Find the critical points of f(x, y) = x⁴ + y⁴ − 16xy, classify them, and give the value fmin of f at its local minimum.
f(x, y) = x⁴ + y⁴ − 16xy
fmin =
Answer key
- 1. fy(−1, 2) = −62
- 2. fx(−1, 1) = 16
- 3. Duf = 2.828
- 4. Duf = 0.7007
- 5. A (0, 0)
- 6. fmin = −32
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