# Homework Help: Linear Functionals

1. Dec 10, 2006

### wurth_skidder_23

I am studying for a final I have tomorrow in linear algebra, and I am still having trouble understanding linear functionals. Can someone help me out with this example problem, walk me through it so I can understand exactly what a linear functional is?

Is the following a linear functional?

$$\ y (x)=\int_0^1\ t^2 x(t) \, dx$$
$$\ y (x)=x(-2)+\int_0^1\ x(t^2)\, dt$$

2. Dec 10, 2006

### StatusX

Always start by going back to the definitions.

3. Dec 10, 2006

### wurth_skidder_23

For the second one, which is basically just an addition to the first, is this correct?

Property 1 of a linear functional is satisfied as follows:
$$\ y (x+z)=x(-2)+z(-2)+\int_0^1\ (x(t^2)+z(t^2))\, dt$$
$$\ y (x+z)=x(-2)+\int_0^1\ x(t^2)\, dt + z(-2)+\int_0^1\ z(t^2)\, dt$$
$$\ y (x+z)=y(x)+y(z)$$

Property 2 of a linear function is satisfied similarly:
$$\ y(a x)=a x(-2)+\int_0^1\ a x(t^2)\, dt$$
$$\ y(a x)=a (x(-2)+\int_0^1\ x(t^2)\, dt)$$
$$\ y(a x)=a y(x)$$

Last edited: Dec 10, 2006
4. Dec 10, 2006

### StatusX

It's as easy as that.