Question

Find dw/ds using the appropriate Chain Rule for w=y^3-4x^2y where x=e^s and y=e^t, and evaluate the partial derivative at s=-3 and t=5 . Round your answer to two decimal places.

Answer 1

Answer:

-2.95

Step-by-step explanation:

Given the functions w=y^3-4x^2y where x=e^s and y=e^t, to get dw/ds, we will use the chain rule for composite functions as shown;

dw/ds = dw/dx*dx/ds + dw/dy*dy/ds

dw/dx = -8xy

dx/ds = e^s

dw/dy = 3y²-4x²

dy/ds = 0 (since there are no s variable in the function)

Substituting the differentials into the formula above;

dw/ds = -8xy(e^s) + 3y²-4x²(0)

dw/ds = -8xy(e^s)

Substituting s = -3 and t = 5 into the resulting function;

dw/ds = -8(e^s)(e^t)(e^s)

dw/ds = -8(e^2s)(e^t)

dw/ds =  -8(e^-6)(e^5)

dw/ds = -8*0.00248*148.413

dw/ds = -2.945 ≈ --2.95 (to 2 dp)