55. f(x,y,z) = x^2 + 2y^2 + 4z^2 + 10; P(1,0,4):
0,
56. f(x,y,z) = 4 - x^2 + 3y^2 + e^(2 - 1): (Vi)
57. f(x,y,z) = 1 + 4xyz; P(-1,-1,-1); ~)
58. f(x,y,z) = xy + yz + xz + 4; P(2,-2,1); (o)
59. f(x,y,z) = 1 + sin(x + 2y - 2); P(1,2,2); (3,3,3)
60. f(x,y,z) = e^(-x); P(0,1,-1); (3,3,3)