The sentence "This is proved" is correct and usable in written English.
You can use it when you want to state something as a fact. For example: "This is proved by the extensive research that has been done."
This is proved in the behavior of the committee and in the meagerness of the public's interest.
This is proved by the color reproduction printed with the article, and any un-starry-eyed viewing of the actual ceiling.
This is proved in a collection of photographs of terror-stricken tots in "Scared of Santa," by Denise Joyce and Nancy Watkins.
This is proved by the audiences for Greg Doran's powerful modern-dress revival in which Tennant turns in an extremely captivating performance.
This is proved only half true when Ivan is abducted by Stark's deadly enemy, Justin Hammer, the unacceptable face of capitalism, played with considerable verve by Sam Rockwell as Batman in a three-piece designer suit.
This is proved, for example, in [14].
This is proved in [9], page 248.
This is proved by the following inequalities.
This is proved by Lemma 5 and 6.
This is proved by their increased spending in the "staying healthy" industry.
This is proved by the theoretical error estimate for different model systems.
