An acute angle is an angle with measure greater than 0 but less than 90 degrees ( radians).
Examples:http://www.google.com/search?q=acute+angle&hl=en&client=safari&rls=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=vppET9XPHOTciQKi95jbDg&ved=0CEgQsAQ&biw=1280&bih=599
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