Answer:
cosA = - [tex]\frac{7}{25}[/tex]
Step-by-step explanation:
Using the double angle identity
cos2A = 2cos²A - 1 , then
cosA = 2cos²([tex]\frac{A}{2}[/tex] ) - 1 , that is
cosA = 2 × ([tex]\frac{3}{5}[/tex] )² - 1
= 2 × [tex]\frac{9}{25}[/tex] - 1
= [tex]\frac{18}{25}[/tex] - [tex]\frac{25}{25}[/tex]
= - [tex]\frac{7}{25}[/tex]
