If cosх A/2 =3/5, find the value of cos A​

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If cosх A/2 =3/5, find the value of cos A​

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Nguyệt Ánh 4 years 2021-07-20T04:15:39+00:00 1 Answers 15 views 0

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  1. giabao
    0
    2021-07-20T04:17:13+00:00
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    Answer:

    cosA = – \frac{7}{25}

    Step-by-step explanation:

    Using the double angle identity

    cos2A = 2cos²A – 1 , then

    cosA = 2cos²(\frac{A}{2} ) – 1 , that is

    cosA = 2 × (\frac{3}{5} )² – 1

            = 2 × \frac{9}{25} – 1

           = \frac{18}{25} – \frac{25}{25}

           = – \frac{7}{25}

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