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Question 46 of 50

Q.Find the differential equation by eliminating the constants a and b from the equation y = eˣ(a+bx²).

West Bengal WbchseWest Bengal HS (WBCHSE) Board 2025Subjective· 2mImportance★★★★★
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Differentiate twice to get two equations, then eliminate aa and bb between them.

Given y=ex(a+bx2)y=e^x(a+bx^2), two constants means we need two derivatives to eliminate them.

First derivative:

y′=ex(a+bx2)+ex(2bx)=y+2bx ex  ⇒  y′−y=2bx ex(∗)y' = e^x(a+bx^2) + e^x(2bx) = y + 2bx\,e^x \;\Rightarrow\; y'-y = 2bx\,e^x \quad(\ast)

Second derivative:

y′′=y′+2b ex+2bx ex=y′+2b ex+(y′−y)y'' = y' + 2b\,e^x + 2bx\,e^x = y' + 2b\,e^x + (y'-y)

⇒  y′′−2y′+y=2b ex(∗∗)\Rightarrow\; y''-2y'+y = 2b\,e^x \quad(\ast\ast)

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