Question

sendo x € 4 quadrante e cosx= ⅕, calcule o cos 2x​

Answer 1

Resposta:

-23/25

Explicação passo-a-passo:

cos²x = (1+cos2x)/2

1/25 = (1+cos2x)/2

2/25 = 1+cos2x

cos2x = 2/25 - 1

cos2x = 2/25 - 25/25

cos2x = -23/25

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outra maneira de fazer

cos²x + sen²x = 1

1/25 + sen²x = 1

sen²x = 1 - 1/25

sen²x = 24/25

cos2x = cos²x - sen²x

cos2x = 1/25 - 24/25

cos2x = -23/24