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Question 121 of 126

Q.The order and degree of the differential equation dydx−4dydx−7x=0\sqrt{\dfrac{dy}{dx}}-4\dfrac{dy}{dx}-7x=0 are respectively :

(a) 1,21, 2
(b) 2,12, 1
(c) 2,22, 2
(d) 1,11, 1
Tamil Nadu DgeTamil Nadu HSC (DGE) Board 2025MCQ· 1mImportance★★★★★
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Isolating the radical and squaring turns the equation into a polynomial in dy/dxdy/dx; the power of the highest derivative after clearing the radical gives the degree.

  1. Given dydx−4dydx−7x=0\sqrt{\dfrac{dy}{dx}}-4\dfrac{dy}{dx}-7x=0. Let p=dydxp=\dfrac{dy}{dx}.
  2. Isolate the radical: p=4p+7x\sqrt p=4p+7x.
  3. Square both sides to remove the radical (a fractional power of a derivative is not allowed for degree to be defined): p=(4p+7x)2=16p2+56px+49x2p=(4p+7x)^2=16p^2+56px+49x^2.
  4. Rearranged: 16p2+(56x−1)p+49x2=016p^2+(56x-1)p+49x^2=0 — a polynomial equation in p=dydxp=\dfrac{dy}{dx}. …

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