Khảo sát cực trị của \[{\rm{z}} = 1 - \sqrt {{{({\rm{x}} - 1)}^2} + {{\rm{y}}^2}} \] tại (1,0):

A. \[\frac{1}{2}({\rm{e}} + {{\rm{e}}^{ - 1}})\]

B. \[\frac{1}{2}({\rm{e}} - {{\rm{e}}^{ - 1}})\]

C. e

D. \[ - \frac{1}{2}({\rm{e}} - {{\rm{e}}^{ - 1}})\]

A. \[ - \frac{1}{2}\]

B. \[\frac{1}{2}\]

C. 0

D. không tồn tại 

A. 1

B. \(\frac{1}{2}\)

C. 0

D. Không tồn tại

A. 0

B. 1

C. 2

D. 3

A. \[{\rm{dz = (2x}} - {\rm{2y + ycos(xy))dx}}\]

B. \[{\rm{dz = (}} - {\rm{2x + xcos(xy))dy}}\]

C. \[{\rm{dz = (}} - {\rm{2x}} - {\rm{2y + ycos(xy))dx + (}} - {\rm{2x + xcos(xy)dy)}}\]

D. \[{\rm{dz = (2x}} - {\rm{2y + cos(xy))dx + (}} - {\rm{2x + cos(xy))dy}}\]

A. 2

B. dx+dy

C. 2(dx+dy)

D. 0

A. \[{\rm{z}}_{{{\rm{x}}^{\rm{3}}}{{\rm{y}}^{{\rm{19}}}}}^{{\rm{22}}}{\rm{ = z}}_{{{\rm{y}}^{\rm{3}}}{{\rm{x}}^{{\rm{19}}}}}^{{\rm{22}}}{\rm{ = 1}}\]

B. \[{\rm{z}}_{{{\rm{x}}^{{\rm{13}}}}{{\rm{y}}^{\rm{9}}}}^{{\rm{22}}}{\rm{ = z}}_{{{\rm{y}}^{\rm{6}}}{{\rm{x}}^{{\rm{16}}}}}^{{\rm{22}}}{\rm{ = 2}}\]

C. \[{\rm{z}}_{{{\rm{x}}^{\rm{7}}}{{\rm{y}}^{{\rm{15}}}}}^{{\rm{22}}}{\rm{ = z}}_{{{\rm{y}}^{\rm{6}}}{{\rm{x}}^{{\rm{16}}}}}^{{\rm{22}}}{\rm{ = 0}}\]

D. \[{\rm{z}}_{{{\rm{x}}^{{\rm{11}}}}{{\rm{y}}^{{\rm{11}}}}}^{{\rm{22}}}{\rm{ = z}}_{{{\rm{y}}^{{\rm{11}}}}{{\rm{x}}^{{\rm{11}}}}}^{{\rm{22}}}{\rm{ = 3}}\]