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Mathematics 9 Online
OpenStudy (anonymous):

I need help with this question involving law of cosines, etc.? Will give medal & fan. "Use the law of cosines to find the value of 2 * 4 * 5 cos theta" A. 40 B. -40 C. 20 D. 37 I used the formula C = cos^-1 (a^2 + b^2 - c^2 / 2ab) and got 108.21, which obviously isn't the answer /:

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