Assignment Set 2 (Due May 21, 2pm) Ruipeng Shen May 20, 2014 2.6.12 Let z = f (r), where r = yzx − xzy = 0 for all (x, y) 6= (0, 0). 2.6.16 p x2 + y 2 and f is a differentiable function. Prove that Let w = f (x, y, z), where x = r cos θ and y = r sin θ. Find ∂w/∂r, ∂w/∂θ and ∂w/∂z. 2.7.20 Determine the maximum rate of change of the function f (x, y, z) = p = (3, 3, 2), and the direction in which it occurs. 4.1.8 √ xyz at the point Find the second partial derivatives zxx , zxy , zyx and zyy of the function z = x arctan(y/x). 4.1.16 Explain why there is no c2 function f (x, y) such that fx (x, y) = ex + xy and fy (x, y) = ex + xy. 4.2.8 Find the second-order Taylor formula for the function f (x) = cos x at the point x0 = π/3. Give the remainder in integral form. 4.2.24 Find the second-order Taylor formula for the function f (x, y) = ln(x2 + y 2 + 1) at the point (0, 1). 4.3.10 Find all critical points (if any) of the given function f (x, y) and determine whether they are local extreme points or saddle points. f (x, y) = x3 + y 3 + 3x2 y − 3y. 4.3.14 Find all critical points (if any) of the given function f (x, y) and determine whether they are local extreme points or saddle points. f (x, y) = ln(x2 + y 2 + 2). 1
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