Question 1030817
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Simplify completely:  √(1 + cos80°​)/2)
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Use the formula for half-argument

{{{sqrt((1+cos(alpha))/2)}}} = {{{cos(alpha/2)}}}

(see the lesson  <A HREF=https://www.algebra.com/algebra/homework/Trigonometry-basics/Trigonometric-functions-of-half-argument.lessonTrigonometric functions of half argument>Trigonometric functions of half argument</A>  in this site).

You will get

{{{sqrt((1+cos(80^o))/2)}}} = {{{cos(40^o)}}}
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