For f(x, y) = 5 sin(−2x + 3y), find the mixed second partial derivative ∂²f/∂x∂y at (1, −1).
Multivariable calculus worksheet with answers
1.Easy
f(x, y) = 5 sin(−2x + 3y)P = (1, −1)
fxy(1, −1) =
2.Easy
For f(x, y) = 3xy − 2y³, find the partial derivative ∂f/∂x at the point (−3, −3).
f(x, y) = 3xy − 2y³P = (−3, −3)
fx(−3, −3) =
3.Medium
z = −xy − 4x² + 4y³ with x = 2t − 2 and y = −t² − 2. Use the chain rule to find dz/dt at t = 2.
z = −xy − 4x² + 4y³x = 2t − 2y = −t² − 2t = 2
dz/dt =
4.Medium
For f(x, y) = xy − x² − 2y³, find the maximum rate of change of f at the point (1, −1), that is |∇f|.
f(x, y) = xy − x² − 2y³P = (1, −1)
|∇f| =
5.Hard
The integral I = ∫01.2 ∫x1.2 cos(y²) dy dx cannot be done in this order. Reverse the order of integration and evaluate it.
f = cos(y²)0 ≤ x ≤ y ≤ 1.2
I =
6.Hard
Find the critical points of f(x, y) = −x³ + 12x − y² − 6y, classify them, and give the value fmax of f at its local maximum.
f(x, y) = −x³ + 12x − y² − 6y
fmax =
Answer key
- 1. fxy(1, −1) = 28.77
- 2. fx(−3, −3) = −9
- 3. dz/dt = −1740
- 4. |∇f| = 5.831
- 5. I = 0.4957
- 6. fmax = 25
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