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Active Calculus - Multivariable

Activity 11.3.2.
In this activity, we will be examining the function \(\displaystyle f(x,y) = \frac{x y^2}{x+1}\) at the point \((1,2)\text{.}\) Specifically, we will be looking how the traces of this function will be related to the values of the partial derivatives.
(a)
Write a formula for the trace \(f(x,2)\) as a function of \(x\text{.}\) On the axes provided, draw the graph of the trace with \(y=2\) around the point where \(x=1\text{.}\) Then sketch the tangent line at the point with \(x=1\) on your graph.
(b)
Compute the partial derivative \(f_x(1,2)\) and relate its value to the sketch you just made.
(c)
Write a formula for the trace \(f(1,y)\) as a function of \(y\text{.}\) On the axes provided, draw the graph of the trace with \(x=1\text{.}\) Then sketch the tangent line at the point with \(y=2\) on your graph.
(d)
Compute the partial derivative \(f_y(1,2)\) and relate its value to the sketch you just made.