Question

cos a=4/5. Найти cos2a

Answer 1

cos2a=2cos^2a-1
cosa=45
cos2a=2*(45)^2-1=2*1625-1=3225-1=32-2525=725=0,28)
Ответ ---- (cos2a=725 или cos2a=0,28)

Answer 2

$cosa= frac{4}{5} \ cos2a=2cos^{2} a-1=2*( frac{4}{5} )^{2} -1=2* frac{16}{25} -1=2*0.64-1= \ =1.28-1=0.28$