Show that the equation of the curve whose slope at any point is equal to y + 2x and which passes through the origin is y + 2(x + 1) = 2e2x.
Given slope at any point = y + 2x
⇒
⇒
We can see that it is a linear differential equation.
Comparing it with
P = – 1, Q = 2x
I.F = e∫Pdx
= e – dx
= e – x
Solution of the given equation is given by
y × I.F = ∫Q × I.F dx + c
⇒ y × e – x = ∫ 2x × e – x dx + c
⇒ ye – x = 2∫ x × e – x dx + c
⇒ ye – x = – 2x e – x – 2 e – x + c
⇒y = – 2x – 2 + cex ……(1)
As the equation passing through origin,
0 = 0 – 2 + c× 1
⇒ c = 2
Putting the value of c in equation (1)
∴ y = – 2x – 2 + 2ex