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Expert: Sherry Wallin - 3/22/2009


Question
if cos A=1/3, find cos 4A     How would you solve this?

Answer
There are probably several ways to conquer this question but here is just one way to do it:
First find out what A is: arccos(cos A) = arccos(1/3)--> A = 70.5288 deg
4(70.5288)= 282.1152 and the cos 4A = cos (282.1152) = .20988
Of course these are all approximations but they are within thousandths of each other.

The basic idea is that the arccosine is the inverse of the cosine and when you have the cosine of an angle you can take the arccosine of the cos of that angle to find the angle. arccosine is just another name for cosine inverse or cos^-1(A)

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Sherry Wallin

Expertise

I can answer most questions up through Calculus and some in Number Theory and Abstract Algebra.

Experience

I have had my Bachelor's Degree since 1987 and have been a teacher since 1988. I earned my Masters Degree in Mathematics May 2010. I have been teaching at the same community college since 2002.

Education/Credentials
I have taught 12 years at the community college level, medical college, and technical college as well as a high school instructor and alternative education instructor and charter school instructor.

Awards and Honors
Master's GPA 3.56 Bachelor's GPA 3.34 Post grad work not degree related GPA 4.0

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