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Question 12 of 43

Q.The order and degree of the differential equation d2ydx2=dydx+5\sqrt{\dfrac{d^2y}{dx^2}} = \sqrt{\dfrac{dy}{dx}} + 5 are respectively :

(a) 22 and 33
(b) 22 and 11
(c) 33 and 22
(d) 22 and 22
Tamil Nadu DgeTamil Nadu HSC (DGE) Commerce Board 2020MCQ· 1mImportance★★★★★
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Order = order of the highest derivative present = 22. To get the degree, remove all radicals: squaring twice makes d2ydx2\frac{d^2y}{dx^2} appear to power 22, so degree = 22.

Given: d2ydx2=dydx+5\sqrt{\dfrac{d^2y}{dx^2}} = \sqrt{\dfrac{dy}{dx}} + 5.

Step 1 — Order. The highest-order derivative is d2ydx2\dfrac{d^2y}{dx^2}, so order =2= 2.

Step 2 — Make it polynomial in the derivatives (needed for degree). Square both sides:

d2ydx2=(dydx+5)2=dydx+10dydx+25.\frac{d^2y}{dx^2} = \left(\sqrt{\frac{dy}{dx}} + 5\right)^2 = \frac{dy}{dx} + 10\sqrt{\frac{dy}{dx}} + 25.

Isolate the remaining radical and square again: …

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