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Syllabus Vector Differentiation - Velocity and Acceleration - Gradient ...

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Engineering Mathematics - II - <strong>Vector</strong> Calculus - 2007<br />

<br />

i j k<br />

<br />

x(<br />

x<br />

F ) <br />

x<br />

y<br />

z<br />

2z 2x 0 2z x<br />

2<br />

<br />

(2x 2) j<br />

31. Find the directional derivative of<br />

x<br />

2<br />

yz 4xz<br />

2<br />

at (1, -2, -1)<br />

<br />

in the direction 2 i j<br />

2 k .<br />

Suggested answer:<br />

<br />

<br />

<br />

(2xyz 4z<br />

2<br />

) i x<br />

2<br />

z j<br />

(x<br />

2<br />

y 8xz) k<br />

<br />

at<br />

(1,<br />

2,<br />

<br />

1)is 8 i j<br />

10 k<br />

Let<br />

<br />

c 2 i j<br />

2 k<br />

Directional derivative in the direction of<br />

<br />

c<br />

is<br />

<br />

(2 i j<br />

2 k)<br />

. c (8 i j<br />

10 k).<br />

3<br />

<br />

1<br />

(16<br />

3<br />

1 20)<br />

37<br />

<br />

3<br />

32. Find the directional derivative of 4xz<br />

3 3x<br />

2<br />

y<br />

2<br />

z at (2, -1, 2)<br />

<br />

in the direction of 2 i 3 j<br />

6 k .<br />

Page 62 of 72

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