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Multiple Choice
Given , where and , use the chain rule to find the partial derivatives and .
A
= , =
B
= , =
C
= , =
D
= , =
Verified step by step guidance
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Step 1: Start by identifying the given function z = (x - y)^7, where x = s^2 t and y = s t^2. To find the partial derivatives ∂z/∂s and ∂z/∂t, we will use the chain rule.
Step 2: Apply the chain rule for ∂z/∂s. The chain rule states that ∂z/∂s = ∂z/∂u * ∂u/∂s, where u = (x - y). First, compute ∂z/∂u = 7u^6 (since z = u^7). Then, compute ∂u/∂s = ∂(x - y)/∂s = ∂x/∂s - ∂y/∂s.
Step 3: Compute ∂x/∂s and ∂y/∂s. For x = s^2 t, ∂x/∂s = 2s t (using the product rule). For y = s t^2, ∂y/∂s = t^2 (using the product rule). Substitute these into ∂u/∂s = ∂x/∂s - ∂y/∂s to get ∂u/∂s = 2s t - t^2.
Step 4: Combine the results to find ∂z/∂s. Substitute ∂z/∂u = 7u^6 and ∂u/∂s = 2s t - t^2 into ∂z/∂s = ∂z/∂u * ∂u/∂s. This gives ∂z/∂s = 7(x - y)^6 (2s t - t^2).
Step 5: Repeat the process for ∂z/∂t. Apply the chain rule: ∂z/∂t = ∂z/∂u * ∂u/∂t. Compute ∂u/∂t = ∂(x - y)/∂t = ∂x/∂t - ∂y/∂t. For x = s^2 t, ∂x/∂t = s^2. For y = s t^2, ∂y/∂t = 2s t. Substitute these into ∂u/∂t = ∂x/∂t - ∂y/∂t to get ∂u/∂t = s^2 - 2s t. Finally, substitute ∂z/∂u = 7u^6 and ∂u/∂t = s^2 - 2s t into ∂z/∂t = ∂z/∂u * ∂u/∂t to get ∂z/∂t = 7(x - y)^6 (s^2 - 2s t).