Class 11

Math

Algebra

Sequences and Series

If $sinβ$ is the geometric mean between $sinα$ $cosα$ then $cos2β$ is equal to :

- $2sin_{2}(4π +α)$
- $1−sin(2α)$
- $2cos_{2}(4π −α)$
- $2sin_{2}(4π −α)$

$∴sinβ=sinα.cosα =41 sin2α $

$Cos2β=1−2sin_{2}β=1−2sinαcosα=1−sin2α$