welphygirl1299 welphygirl1299

11-08-2017
Mathematics

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What is the best first step if your plan is to find the exact value of cos 75Â°using the cosine angle sum identity?

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Аноним Аноним

11-08-2017

cos 75 = cos (45 + 30) = cos45 cos30 - sin45 sin30

= 1/ sqrt2 * sqrt3/2 - 1/ sqrt2 * 1/2

= sqrt3 / 2 sqrt2 - 1 / 2 sqrt2

= sqrt3 - 1
-------------
2 sqrt2

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