Question

Determine o cos 2x
sendo sen x = 3/5

Answer 1

$\boxed{\begin{array}{l}\sf cos(2x)=1-2sen^2(x)\\\sf cos(2x)=1-2\cdot\bigg(\dfrac{3}{5}\bigg)^2\\\sf cos(2x)=1-2\cdot\dfrac{9}{25}\\\sf cos(2x)=1-\dfrac{18}{25}\\\sf cos(2x)=\dfrac{25-18}{25}\\\sf cos(2x)=\dfrac{7}{25}\end{array}}$