Samyak Jain
Last Activity: 5 Years ago
(ex + 1)ydy – (y2 + 1)exdx = 0
ydy/(y2 + 1) = ex dx /(ex + 1) 2ydy/(y2 + 1) = 2ex dx /(ex + 1)
Now if y2 + 1 = t, then differentiating both sides we get 2ydy = dt
and similarly ex + 1 = u, then ex dx = du
dt / t = 2 du / u . Integratin both sides, we get
ln(t) = 2 ln(u) + lnc , where I’ve taken lnc as constant of integration and ln(t) means loge(t).
ln(t) – 2 ln(u) = lnc i.e. ln(t) – ln(u)2 = lnc or ln(t/u2) = lnc
t/u
2 = c [using rules of logarithm]
Substitute t as y2 + 1 and u as ex + 1 to get
(y2 + 1)/(ex + 1)2 = c [You can rearrange the result to get the desired answer.]