# Toronto Math Forum

## MAT244--2018F => MAT244--Tests => Quiz-3 => Topic started by: Victor Ivrii on October 12, 2018, 06:09:32 PM

Title: Q3 TUT 5101
Post by: Victor Ivrii on October 12, 2018, 06:09:32 PM
Find the Wronskian of two solutions of the given differential equation without solving the equation.
$$(1-x^2)y''-2xy'+\alpha(\alpha+1)y=0, \qquad\text{Legendre's equation}.$$
Title: Re: Q3 TUT 5101
Post by: Yiran Zhu on October 12, 2018, 06:21:57 PM
This is the hand written solution. I am still trying to figure out how to convert latex into plain text.
Title: Re: Q3 TUT 5101
Post by: Yiting Zhang on October 12, 2018, 06:26:58 PM
$$y′′−\frac{2x}{1−x^2}y′+\frac{\alpha(\alpha+1)}{1−x^2}y=0$$
$$W=ce^{\int −p(x) dx}, p(x) = −\frac{2x}{1−x^2}$$
$$W = ce^{\int \frac{2x}{1−x^2} dx}$$
$$u=1−x^2, du=−2xdx$$
$$ce^{-\int \frac{1}{u}du} = ce^{-ln(u)+C}=ce^{−ln(1−x^2)+C}=\frac{ce^C}{1-x^2}$$
Since $ce^C$ is constant. Let $ce^C = c$
$$W=\frac{c}{1−x^2}$$
Title: Re: Q3 TUT 5101
Post by: Victor Ivrii on October 12, 2018, 07:36:47 PM
Yiran, you use LaTeX math snippets on the forum
Yiting: ln must be escaped as \ln