Replying to the question should the left arm be kept straight
NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO

Absolutely NOT

The majority of tour players bend their left arm 20 degrees at the top of the back swing

By keeping the left arm straight you create tension and instead of increasing your ARC WIDTH you are actually ddecreasing it. This happens because on the way down to the ball since you're arms are so tense they cinch in towards your body by decreasing arc width. The result a thin shot if not worse.

The left arm naturally straightens out on the way down to the ball

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Jordy Scerbo
Golf Instructor