"determined to be invalid" is correct and usable in written English.
You can use it when you want to express the idea that something has been observed and declared to be untrue or no longer applicable. For example, "The previously-held hypothesis was determined to be invalid after further analysis."
Campaigns routinely gather far more signatures than required because many are determined to be invalid.
Treatment with NSAIDs was determined to be invalid.
The jury found that Apple had indeed violated the three patents, which were not determined to be invalid, after deliberating for four hours according to Bloomberg news.
A phone number written on the back of the cashed checks was determined to be invalid.
The agreement entitled Evergreen to 33% of Yao's earnings, but the contract was later determined to be invalid.
In the event that any provision is determined to be invalid or otherwise unenforceable or illegal, these Official Rules will otherwise remain in effect and will be construed in accordance with their terms as if the invalid or illegal provision were not contained herein.
Pharmaceutical data appeared to be invalid (see " Results").
In addition, samples from males in our study were twice as likely as samples from females to contain no amplifiable DNA, as determined by the absence of the cellular housekeeping gene, and therefore to be invalid for HPV detection.
This approach is likely to be invalid if the parcel characteristics that determine property values also influence the government's decision about how to implement regulations.
If a court found any part of the act to be invalid, the entire legislation would also be invalid.
The argument forms we showed to be invalid in Adams's logic (§3.2) are invalid on Stalnaker's semantics.
