cos=-4/5 180 найдите cos2a

cos=-4/5
180 найдите cos2a
- Предмет:
  Алгебра
- Автор:
  dottieozxc
- 6 лет назад

Ответы 1

$cos2a=cos ^{2} a-sin ^{2} s=cos ^{2} a- \\ -(1-cos ^{2} a)=cos ^{2} a-1+cos ^{2} a=\\=2cos ^{2} a-1 \\ \\ cosa=- \frac{4}{5} \\ \\ 2*(- \frac{4}{5} ) ^{2} -1=2* \frac{16}{25} -1= \frac{32}{25} - \frac{25}{25} =\\\\= \frac{7}{25} = \frac{7*4}{25*4} = \frac{28}{100} =0.28$
- Автор:
  stella10
- 6 лет назад
- 0
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cos=-4/5 180 найдите cos2a

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cos=-4/5
180 найдите cos2a