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Question: Answered & Verified by Expert
If $u \equiv u(x, y)=\sin (y+a x)-(y+a x)^2$, then it implies
MathematicsDifferentiationTS EAMCETTS EAMCET 2011
Options:
  • A $u_{x x}=a^2 \cdot u_{y y}$
  • B $u_{y y}=a^2 u_{x x}$
  • C $u_{x x}=-a^2 \cdot u_{y y}$
  • D $u_{y y}=-a^2 u_{x x}$
Solution:
1329 Upvotes Verified Answer
The correct answer is: $u_{x x}=a^2 \cdot u_{y y}$


On differentiating partially w.r.t. $x$, we get
$u_x=\cos (y+a x) a-2(y+a x) a$
Again differentiating partially w.r.t. $x$, we get

On differentiating partially Eq. (i) w.r.t. $y$, we get
$u_y=\cos (y+a x)-2(y+a x)$

$\therefore$ From Eqs. (ii) and (iii), we get
$u_{x x}=a^2 u_{y y}$

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