Sign in
Please select an account to continue using cracku.in
↓ →
Join Our JEE Preparation Group
Prep with like-minded aspirants; Get access to free daily tests and study material.
If $$\frac{dy}{dx} + \frac{2^x y(2y-1)}{2^x - 1} = 0, x, y > 0, y(1) = 1$$, then $$y(2)$$ is equal to
Given,
$$\frac{dy}{dx}+\frac{2^{x-y}(2^y-1)}{2^x-1}=0$$
Rearranging,
$$\frac{dy}{dx}=-\frac{2^x(2^y-1)}{2^y(2^x-1)}$$
$$\frac{2^y}{2^y-1}\,dy=-\frac{2^x}{2^x-1}\,dx$$
Integrating both sides,
$$\int\frac{2^y}{2^y-1}\,dy=-\int\frac{2^x}{2^x-1}\,dx$$
Using
$$\int\frac{2^t}{2^t-1}\,dt=\frac1{\ln2}\ln(2^t-1)$$
we get
$$\ln(2^y-1)+\ln(2^x-1)=C$$
$$ (2^y-1)(2^x-1)=k $$
Using the condition
$$y(1)=1$$
we get
$$ (2^1-1)(2^1-1)=k $$
$$k=1$$
Hence,
$$ (2^y-1)(2^x-1)=1 $$
Now, at
$$x=2$$
$$ (2^y-1)(4-1)=1 $$
$$3(2^y-1)=1$$
$$2^y=\frac43$$
$$y=\log_2\frac43$$
$$y=2-\log_23$$
Hence,
$$\boxed{2-\log_23}$$
Create a FREE account and get:
Educational materials for JEE preparation