Let f(x, y) = 1 + x ln(xy — 5). (a) Explain why the function is differentiable at the point (2, 3) (b) Find the equation of the tangent plane at the point (2,3).

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### Differentiability and Tangent Plane of a Given Function

#### Problem Statement
Consider the function \( f(x, y) = 1 + x \ln(xy - 5) \).

**Tasks:**

**(a)** Explain why the function is differentiable at the point (2, 3).

**(b)** Find the equation of the tangent plane at the point (2, 3).


#### Solutions

**(a) Differentiability at the Point (2, 3):**
To determine whether the function \( f(x, y) \) is differentiable at the point (2, 3), we need to check the existence and continuity of the partial derivatives of \( f \) at that point. Specifically, the partial derivatives with respect to \( x \) and \( y \) must exist and be continuous at (2, 3).

**(b) Equation of the Tangent Plane:**
To find the equation of the tangent plane to the surface defined by \( f(x, y) \) at the point (2, 3), we use the formula for the tangent plane of a function of two variables. The formula is:

\[ z = f(a, b) + f_x(a, b)(x - a) + f_y(a, b)(y - b) \]

where \( (a, b) \) is the point of tangency, \( f_x \) and \( f_y \) are the partial derivatives of \( f \) with respect to \( x \) and \( y \), respectively.

1. Calculate \( f_x \) and \( f_y \) at the point (2, 3).

2. Evaluate \( f(2, 3) \).

3. Plug in these values into the tangent plane formula to get the equation.
Transcribed Image Text:### Differentiability and Tangent Plane of a Given Function #### Problem Statement Consider the function \( f(x, y) = 1 + x \ln(xy - 5) \). **Tasks:** **(a)** Explain why the function is differentiable at the point (2, 3). **(b)** Find the equation of the tangent plane at the point (2, 3). #### Solutions **(a) Differentiability at the Point (2, 3):** To determine whether the function \( f(x, y) \) is differentiable at the point (2, 3), we need to check the existence and continuity of the partial derivatives of \( f \) at that point. Specifically, the partial derivatives with respect to \( x \) and \( y \) must exist and be continuous at (2, 3). **(b) Equation of the Tangent Plane:** To find the equation of the tangent plane to the surface defined by \( f(x, y) \) at the point (2, 3), we use the formula for the tangent plane of a function of two variables. The formula is: \[ z = f(a, b) + f_x(a, b)(x - a) + f_y(a, b)(y - b) \] where \( (a, b) \) is the point of tangency, \( f_x \) and \( f_y \) are the partial derivatives of \( f \) with respect to \( x \) and \( y \), respectively. 1. Calculate \( f_x \) and \( f_y \) at the point (2, 3). 2. Evaluate \( f(2, 3) \). 3. Plug in these values into the tangent plane formula to get the equation.
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