What does "You know it to be true" mean? Is it grammatically correct?

Question

I came across this example. In the book, the girl deceives and convinces the main character of her goals and at the end says :

You know it to be true.

I have a question, why is there no is here?

You know it is true.

I know what else you can say:

You know it is to be true.

But why is it just to be in my example? I will be glad to help you

Answer 1

It's formal English.

You know it to be true.

means

You know that it is true.

Other examples:

I have always known Sarah to be (=known that Sarah is) an honest woman, so I believe what she says.

The authorities know him to be (=know that he is) a cocaine dealer.

It's often used passively:

The pilots were experienced and known to be very competent.

Although it is the most commonly used operating system in the country, within tech circles it is known to be sloppy and inefficient.

^{It turns out to be a Star Wars quote, I am ashamed I didn't know it.}