For f(x, y) = x²y² + 4x² − 2y² + 2xy, find the partial derivative ∂f/∂x at the point (3, −1).
Multivariable calculus worksheet with answers
1.Easy
f(x, y) = x²y² + 4x² − 2y² + 2xyP = (3, −1)
fx(3, −1) =
2.Easy
For f(x, y) = 5xy³ − 4x³ − xy, find the partial derivative ∂f/∂y at the point (1, 3).
f(x, y) = 5xy³ − 4x³ − xyP = (1, 3)
fy(1, 3) =
3.Medium
For f(x, y) = xy³ + 5y³ + 4xy, find the directional derivative Duf at (3, 2) in the direction of v = (3, 0).
f(x, y) = xy³ + 5y³ + 4xyP = (3, 2)v = (3, 0)
Duf =
4.Medium
For f(x, y) = −2x³y² − x³ − 4y² − 3xy, find the maximum rate of change of f at the point (2, −1), that is |∇f|.
f(x, y) = −2x³y² − x³ − 4y² − 3xyP = (2, −1)
|∇f| =
5.Hard
f(x, y) = x⁴ + y⁴ − 16xy has a critical point at (0, 0). Compute the discriminant D = fxxfyy − fxy² there.
f(x, y) = x⁴ + y⁴ − 16xyP = (0, 0)
D =
6.Hard
Use polar coordinates to evaluate I = ∬R e−(x² + y²) dA, where R is the upper half of the disc x² + y² ≤ 4 (y ≥ 0).
f = e−(x² + y²)0 ≤ r ≤ 20 ≤ θ ≤ π
I =
Answer key
- 1. fx(3, −1) = 28
- 2. fy(1, 3) = 134
- 3. Duf = 16
- 4. |∇f| = 47.38
- 5. D = −256
- 6. I = 1.542
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