※ 引述《j19880706 (smallpig)》之銘言：
: An equation of the tangent plane to the surface , z=2X^2 +Y^2 at the point
: (1,1,3) is _________
: 這題怎麼算教教我
: 感謝大大
Z=2X^2 +Y^2 => f = 2X^2 +Y^2-Z = 0
gradf= 4x i + 2y j - k
N vector = gradf(1,1,3)= 4 i + 2 j - k
tangent plane: 4(x-1)+2(y-1)-(z-3)= 0
=>4x + 2y -z =3
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