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```        pls help me ,I couldnt solve these
q1: if y=ex+e^x+e^x+...........∞,then dy/dx equals
q2:if x=at2 and y=2at then (xy*d2y/dx2)  is equal to
thank u```
6 years ago

419 Points
```										Dear Rishabh
I think there is some mistake in question 1
confirm the qustion and try to do it by taking log
question2
dy/dx= (dy/dt)/(dx/dt)
dy/dt=2a
dx/dt=2at
dy/dx=1/t
d2y/dx2= d/dx(dy/dx)
use chain rule
d2y/dx2= d/dt(dy/dx)*dt/dx
=d/dt(1/t)*1/2at
=-(1/t2)*1/2at
=-1/2at3
xyd2y/dx2=at2*2at*(-1/2at3)= -a

All the best.
AKASH GOYAL

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```
6 years ago
510 Points
```										1)
y=ex+e^x+e^x+...........∞
Y =ex+y
dy/dx = ex+y(1+dy/dx)
dy/dx = (ex+y/1-ex+y )

2)
x=at2 ...........1
y=2at    ..............2
x/y = t/2   .........3
put t in eq 2
y = 4ax/y
y2 = 4ax
now differentiating above eq
2ydy/dx = 4a         .............1
again differentiating
2[(dy/dx)2 +yd2y/dx2] = 0
d2y/dx2 = -(dy/dx)2/y          ..........2
multiply above eq by xy
(d2y/dx2)xy = -x(dy/dx)2
=-x(2a/y)2                    (from eq 1)
approve if u like my ans

```
6 years ago
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