Question

Suppose that f(x,y) is a smooth function and that its partial derivatives have the values, fx(8,5)=2 and fy(8,5)=2. Given that f(8,5)=−2, use this information to estimate the value of f(9,6).

Answer 1

Answer:

f(9,6) = 2

Step-by-step explanation:

We know df = (df/dx)dx + (df/dy)dy

From the question, df/dx = fx(8,5) = 2 and df/dy = fy(8,5) = 2

Since we need to find f(9,6) and f(8,5) = -2

dx = 9 - 8 = 1 and dy = 6 - 5 = 1

f(9,6) = f(8,5) + df

df = (df/dx)dx + (df/dy)dy

df = fx(8,5)dx + fy(8,5)dy

Substituting the values of fx(8,5) = 2, fy(8,5) = 2, dx = 1 and dy = 1

df = 2 × 1 + 2 × 1

df = 2 + 2

df = 4

f(9,6) = f(8,5) + df

substituting the value of df  and f(8,5) into the equation, we have

f(9,6) = -2 + 4

f(9,4) = 2

The value of f(9,6) = 2