Question

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

Answer 1

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

       = $\frac{18}{25}$ - $\frac{25}{25}$

       = - $\frac{7}{25}$