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Problem 1
For each function, evaluate (a) \(f(0,0)\); (b) \(f(1,0) ;\) (c) \(f(0,-1)\); (d) \(f(a, 2) ;\) (e) \(f(y, x)\);(f) \(f(x+h, y+k)\) HINT [See Quick Examples page 1080.] $$ f(x, y)=x^{2}+y^{2}-x+1 $$
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Sketch the graph of a function that has one extremum and no saddle points.
The Gym Shirt Company manufactures cotton socks. Production is partially automated through the use of robots. Daily operating costs amount to $$\$ 150$$ per laborer and $$\$ 60$$ per robot. The number of pairs of socks the company can manufacture in a day is given by a Cobb-Douglas production formula $$ q=50 n^{0.6} r^{0.4} $$ where \(q\) is the number of pairs of socks that can be manufactured by \(n\) laborers and \(r\) robots. Assuming that the company has a daily operating budget of $$\$ 1,500$$ and wishes to maximize productivity, how many laborers and how many robots should it use? What is the productivity at these levels? HINT [See Example 5.]
Find the point on the plane \(2 x-2 y-z+1=0\) closest to \((1,1,0)\).
Let \(H=f_{x x}(a, b) f_{y y}(a, b)-f_{x y}(a, b)^{2} .\) What condition on \(H\) guarantees that \(f\) has a relative extremum at the point \((a, b) ?\)
Locate and classify all the critical points of the functions. HINT [See Example 2.] $$ f(x, y)=x y+\frac{2}{x}+\frac{2}{y} $$
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