Solving a separable integral equation: $y(x) = 1+\int_{1}^{x} \frac{y(t)dt}{t(t+1)}dt$

443 Views Asked by At

Solving integral equation. My answer is wrong. Where do I make a mistake?

$$y(x) = 1+\int_{1}^{x} \frac{y(t)dt}{t(t+1)}dt $$

$$ y'(x) = \frac{d}{dx} \int_{1}^{x} \frac{y(t)dt}{t(t+1)}dt$$

$$ \frac{dy}{dx} = \frac{y(x)}{x(x+1)}$$

$$ \frac{1}{y} = \frac{1}{x(x+1)}dx$$

$$ \int\frac{1}{y} = \int\frac{1}{x(x+1)}dx$$

$$ ln|y| = ln|x|-ln|x+1|+C$$

By y(1) = 1 from the original equation.

$$ C = ln|2| $$

$$ ln|y| = ln|x|-ln|x+1|+ln|2|$$

$$ y = e^{ln|x|-ln|x+1|+ln|2|}$$

$$ y = -x(x+1)ln|2|$$

But the correct answer is $$ y = \frac{2x}{x+1}$$

1

There are 1 best solutions below

1
On BEST ANSWER

From $$ y = e^{\ln|x|-\ln|x+1|+\ln|2|}$$ you may write $$ y = e^{\ln|2x|-\ln|x+1|}=e^{\ln\left|\frac{2x}{x+1}\right|}= \frac{2x}{x+1}.$$