You don’t need to use the exact keyphrase always. Google has the ability to understand similar words and sentences. The ability of Google to understand such a thing is known as keyword stemming.
For example– buy, bought, buying, buys are similar. Don’t ever think Google is a fool. You may think- “This article will not rank for this keyphrase if I don’t use the exact term”
The reality is, Google and other search engines always value user satisfaction, not the exact match or, simple rule of thumb. Write content for readers, it will obviously rank better for similar search terms.
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So, keyword prominence and proximity will work only if the content works better from the readers’ perspective. Any sort of attempt to manipulate Google search results will bring a penalty for your website. Google, sometimes gives a demotion is ranking due to unnatural practice.