This is the 17628th most frequent Russian word.
убедительной
Convincing.
The word "убедительной" is used as an adjective modifying "речью" (speech) to describe it as convincing or persuasive.
Она произнесла убедительной речью.
She delivered a convincing speech.
Here, "убедительной" describes "демонстрацией" (demonstration), emphasizing its capacity to convince or support the theory.
Его доказательства были очень убедительной демонстрацией теории.
His evidence was a very convincing demonstration of the theory.
In this sentence, "убедительной" characterizes "интерпретацией" (interpretation), indicating its ability to persuasively portray the events.