For f(x, y) = 3y·e3xy, find the mixed second partial derivative ∂²f/∂x∂y at (−1, 2).
Multivariable calculus worksheet with answers
1.Easy
f(x, y) = 3y·e3xyP = (−1, 2)
fxy(−1, 2) =
2.Easy
For f(x, y) = 3 sin(2x + 2y), find the mixed second partial derivative ∂²f/∂x∂y at (2, −1).
f(x, y) = 3 sin(2x + 2y)P = (2, −1)
fxy(2, −1) =
3.Medium
z = 3 ln(x² + 4y²) with x = −t − 1 and y = 2t². Use the chain rule to find dz/dt at t = 2.
z = 3 ln(x² + 4y²)x = −t − 1y = 2t²t = 2
dz/dt =
4.Medium
For f(x, y) = 3x³e3y, find the directional derivative Duf at P(2, 0) in the direction towards Q(6, 4).
f(x, y) = 3x³e3yP = (2, 0)Q = (6, 4)
Duf =
5.Hard
Find the critical points of f(x, y) = x³ − 3x + y² − 2y, classify them, and give the value fmin of f at its local minimum.
f(x, y) = x³ − 3x + y² − 2y
fmin =
6.Hard
Evaluate I = ∬T (3x + 2y) dA over the triangle T bounded by y = 0, x = 4 and y = x.
f = 3x + 2y0 ≤ x ≤ 40 ≤ y ≤ x
I =
Answer key
- 1. fxy(−1, 2) = −0.1785
- 2. fxy(2, −1) = −10.91
- 3. dz/dt = 5.864
- 4. Duf = 76.37
- 5. fmin = −3
- 6. I = 85.33
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