For f(x, y) = x²y² + 4x³ + y³ + 4xy, find the partial derivative ∂f/∂x at the point (3, 1).
Multivariable calculus worksheet with answers
1.Easy
f(x, y) = x²y² + 4x³ + y³ + 4xyP = (3, 1)
fx(3, 1) =
2.Easy
Evaluate I = ∫13 ∫23 (2x²y² − 3) dy dx over the rectangle 1 ≤ x ≤ 3, 2 ≤ y ≤ 3.
f = 2x²y² − 31 ≤ x ≤ 32 ≤ y ≤ 3
I =
3.Medium
z = −4x²y² − x² − 4y³ + 4xy with x = t − 1 and y = −2t² − 1. Use the chain rule to find dz/dt at t = 0.
z = −4x²y² − x² − 4y³ + 4xyx = t − 1y = −2t² − 1t = 0
dz/dt =
4.Medium
For f(x, y) = xy − 5x² − 5y², find the directional derivative Duf at (−2, 3) in the direction of v = (4, 3).
f(x, y) = xy − 5x² − 5y²P = (−2, 3)v = (4, 3)
Duf =
5.Hard
f(x, y) = x⁴ + y⁴ − 16xy has a critical point at (2, 2). Compute the discriminant D = fxxfyy − fxy² there.
f(x, y) = x⁴ + y⁴ − 16xyP = (2, 2)
D =
6.Hard
The marked points are the critical points of f(x, y) = x³ + y³ + 6xy. Click the local maximum.
f(x, y) = x³ + y³ + 6xy
- 1A (−2, −2)
- 2B (0, 0)
Answer key
- 1. fx(3, 1) = 118
- 2. I = 103.8
- 3. dz/dt = 6
- 4. Duf = −0.8
- 5. D = 2048
- 6. A (−2, −2)
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