CBSE Class 12 Math 2012 Solved Paper

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Question : 22 of 29
 
Marks: +1, -0
Find the particular solution of the following differential equation:
(x + 1) dydx = 2e−y - 1 ; y = 0 when x = 0
Solution:
(x + 1) dydx = 2e−y - 1
⇒ dy2e−y−1 = dxx+1
⇒ ey2−ey = dxx+1
Integrating both sides, we get:
∫ eydy2−ey = log |x + 1| + log C ... (1)
Let 2 - ey = t
∴ ddy(2−ey)={dt}/{dy}$$
⇒ - ey = dtdy
⇒ ey dy = - dt
Substituting this value in equation 1 , we get:
∫ - dtt = log |x + 1| + log C
⇒ - log |t| = log |C (x + 1)|
⇒ - log |2 - ey| = log |C (x + 1)|
⇒ 12−ey = C (x + 1)
⇒ 2 - ey = 1C(x+1) ... (2)
Now, at x = 0 and y = 0, equation 2 becomes:
⇒ 2 - 1 = 1C
⇒ C = 1
Substituting C = 1 in equation 2 , we get:
2 - ey = 1x+1
⇒ ey = 2 - 1x+1
⇒ ey = 2x+2−1x+1
⇒ ey = 2x+1x+1
⇒ y = log |2x+1x+1| , (x ≠ - 1)
This is the required particular solution of the given differential equation.
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