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Scores on a university exam are normally distributed with a mean of 78 and a standard deviation of 8. the professor teaching the class declares that a score of 70 or higher is required for a grade of at least “c.” using the 68-95-99.7 rule, what percentage of students failed to earn a grade of at least “c”?

Math question.. plz me .. best answer all

Cos^2x+cos^2(120°+x)+cos^2(120°-x)i need this asap. pls me